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The immune system is a network of cells, tissues, and organs that defends the body against attacks by foreign invaders. These invaders are primarily microbes—tiny organisms such as bacteria, parasites, and fungi— that can cause infections. Viruses also cause infections, but are too primitive to be classified as living organisms. The human body provides an ideal environment for many microbes. It is the immune system’s job to keep the microbes out or destroy them. The immune system is amazingly complex. It can recognize and remember millions of different enemies, and it can secrete fluids and cells to wipe out nearly all of them. The secret to its success is an elaborate and dynamic communications network. Millions of cells, organized into sets and subsets, gather and transfer information in response to an infection. Once immune cells receive the alarm, they produce powerful chemicals that help to regulate their own growth and behavior, enlist other immune cells, and direct the new recruits to trouble spots. Although scientists have learned much about the immune system, they continue to puzzle over how the body destroys invading microbes, infected cells, and tumors without harming healthy tissues. New technologies for identifying individual immune cells are now allowing scientists to determine quickly which targets are triggering an immune response. Improvements in microscopy are permitting the first-ever observations of living B cells, T cells, and other cells as they interact within lymph nodes and other body tissues. In addition, scientists are rapidly unraveling the genetic blueprints that direct the human immune response, as well as those that dictate the biology of bacteria, viruses, and parasites. The combination of new technology with expanded genetic information will no doubt reveal even more about how the body protects itself from disease.
What is the author's primary purpose in writing the essay?
- A. to persuade
- B. to analyze
- C. to inform
- D. to entertain
Correct Answer: C
Rationale: The correct answer is 'C: to inform.' The essay provides detailed information about the immune system, its functions, complexities, and the ongoing research in the field. The author's main goal is to educate and increase the reader's understanding of how the immune system works and its significance in protecting the body from diseases. There is no attempt to persuade, analyze for evaluation, or entertain the audience; instead, the focus is on imparting knowledge and insights about the immune system.
You may also like to solve these questions
Subjective exams measure your ability in several areas. Besides recall information, you must be
able to realize content logically and intelligently express yourself in a clearly understood manner. Subjective test provide opportunity for students to show their broad knowledge of a subjective
area. Answers may be in the form of paragraphs or lengthy essays. When your review for an essay exam, concentrate on main ideas rather than details. Since essay tests are less to a few questions, they are likely to deal with more important ideas of a subject. Prepare a list of question you think might be asked. Write an answer to each of your questions. Rather than writing complete sentence down your thoughts in outline form. Doing so will help
you organize the information so that you can express yourself clearly.
When you take the test, read through all the questions before you start to write. Allot time for each question, spending more time for questions worth the most points. Read each question carefully to determine exactly what they are asked. Pay attention to words such as define, illustrate, explain, list, compare, and contrast. Each work requires a different type of response. Write a brief outline of your answer on scrap paper or the back of the test. Make sure you include all the important ideas that are within the limits of the question. In other words, do not write more than is asked for each answer. When you write your answer, keep it specific and as brief as possible. In the introductory sentence it is often helpful to make a general statement that includes
important points addressed in each question. Such a topic sentence serves as a framework for your answer. Then use your outline to develop the main point and subtopics. Add substance to
your answer by including as many facts as possible to support your answer.
Check your paper before you submit it. Look for mistakes in grammar, spelling, sentence
structure, and punctuation. Unless you are certain an answer is wrong, do not change it. Your answer is an educated guess and is usually your best chance of answering correctly.
In the above passage, the word 'subjective' refers to test questions that:
- A. Allow you to choose an answer
- B. Are matching
- C. Are true or false
- D. Require you to write your own answer
Correct Answer: D
Rationale: The term 'subjective' in the passage refers to test questions that require you to write your own answer, as mentioned in the text. Subjective tests typically involve expressing your understanding and knowledge in your own words, often through paragraphs or essays. This type of assessment allows students to demonstrate their comprehension and analytical skills by formulating responses based on their interpretation of the content, rather than selecting from predefined options. Therefore, the correct answer is D: 'Require you to write your own answer.'
Have you ever wondered why the whistle of a traveling, distant locomotive predicts its approach several yards before anyone actually sees it? Or why an oncoming ambulance's screaming siren is heard momentarily several feet before the ambulance comes into full view, before it passes you, and why its siren is still heard faintly well after the ambulance is out of sight?
What you are witnessing is a scientific phenomenon known as the Doppler Effect. What takes place is truly remarkable. In both of these instances, when the train or ambulance moves toward the sound waves in front of it, the sound waves are pulled closer together and have a higher frequency. In either instance, the listener positioned in front of the moving object hears a higher pitch. The ambulance and locomotive are progressively moving away from the sound waves behind them, causing the waves to be farther apart and to have a lower frequency. These fast-approaching modes of transportation distance themselves past the listener, who hears a lower pitch.
What is the main idea of the passage?
- A. Trains and ambulances emit loud noises.
- B. Low-frequency waves produce high-pitched sounds.
- C. High-frequency waves result in low-pitched sounds.
- D. The Doppler Effect explains why sound is heard more strongly initially and then faintly after a moving object has passed.
Correct Answer: D
Rationale: The main idea of the passage is to explain the scientific phenomenon known as the Doppler Effect. The passage describes how when a train or ambulance moves towards a listener, sound waves are compressed, resulting in a higher frequency and pitch. Conversely, as the objects move away, the sound waves stretch, leading to a lower frequency and pitch. The Doppler Effect is the reason why sound is heard louder as the object approaches and then fades as it moves away. This explanation aligns with choice D, making it the correct answer.
A BIT ABOUT BICYCLES
Today, bicycles are so common that it's hard to believe they haven't always been around. But two hundred years ago, bicycles didn't even exist, and the first bicycle, invented in Germany in 1818, was nothing like our bicycles today. It was made of wood and didn't even have pedals. Since then, however, numerous innovations and improvements in design have made the bicycle one of the most popular means of recreation and transportation around the world. In 1839, Kirkpatrick Macmillan, a Scottish blacksmith, dramatically improved upon the original bicycle design. Macmillan's machine had tires with iron rims to keep them from getting worn down. He also used foot-operated cranks like pedals, so his bicycle could be ridden at a quick pace. It didn't look much like a modern bicycle, though, because its back wheel was substantially larger than its front wheel. In 1861, the French Michaux brothers took the evolution of the bicycle a step further by inventing an improved crank mechanism. Ten years later, James Starley, an English inventor, revolutionized bicycle design. He made the front wheel many times larger than the back wheel, put a gear on the pedals to make the bicycle more efficient, and lightened the wheels by using wire spokes. Although this bicycle was much lighter and less tiring to ride, it was still clumsy, extremely top heavy, and ridden mostly for entertainment. It wasn't until 1874 that the first truly modern bicycle appeared on the scene. (14) Invented by another Englishman, H.J. Lawson, the "safety bicycle" would look familiar to today's cyclists. This bicycle had equal-sized wheels, which made it less prone to toppling over. Lawson also attached a chain to the pedals to drive the rear wheel. With these improvements, the bicycle became extremely popular and useful for transportation. Today they are built, used, and enjoyed all over the world.
What was the author's intention in the text?
- A. Learn about repairing modern bicycles
- B. Understand the history of bicycles
- C. Compare various types of bicycles
- D. Discover the latest bicycle technologies
Correct Answer: B
Rationale: The correct answer is B: Understand the history of bicycles. The passage provides a detailed historical account of the evolution of bicycles over time, from their early designs without pedals to the development of the modern 'safety bicycle.' The author's intention is to educate readers about the origins and transformations in bicycle design, highlighting key innovations and improvements that have shaped bicycles into the popular means of transportation and recreation they are today. The text does not focus on repairing bicycles, comparing different types, or discussing the latest technologies, making these choices incorrect.
Lightning Strikes: The old wives' tale of "Lightning never strikes twice" has been proven untrue time and time again. Lightning forms from negative and positive charges within clouds and from the earth below. When these charges react with each other, the air between the cloud and the earth ionizes, which produces a lightning flash. Lightning is actually a series of multiple events consisting of a leader stroke of lightning, followed by as many as 40 smaller strokes of lightning. Being just split seconds apart, these strokes of lightning often reflect off the lining of the clouds.
Lightning rods that extend from above the roof to the ground protect buildings by forming a low resistance path for the lightning so that the lightning does not enter the building, but rather defuses as it penetrates the ground.
Some myths about lightning need to be explained. Lightning does strike tall buildings often, and during a particularly violent storm, a tall building may be hit by lightning several times. The safest place during a thunder and lightning storm is in a metal car or lying flat, face down, in the open, not under a tree as the myth suggests.
Many people believe that thunder and lightning are connected; however, this proves to be true only about 50% of the time, so if you're waiting for the clap of thunder, you're missing out on some exciting strokes of lightning!
Lightning causes injuries, deaths, and forest fires each year. However, some scientists reveal the positive aspects of lightning because it releases nitrogen into the atmosphere which the raindrops then deliver to earth to fertilize our soil.
When taking cover from lightning, you should
- A. go to the highest point in a tall building.
- B. stand in the doorway of a building.
- C. stand under a large tree with branches.
- D. get into a metal car or lie flat on the ground in the open.
Correct Answer: D
Rationale: The correct answer is D: get into a metal car or lie flat on the ground in the open. When taking cover from lightning, it is crucial to minimize your risk of being struck. Getting into a metal car provides protection as the metal shell of the car acts as a Faraday cage, directing the lightning around the vehicle and into the ground. Lying flat on the ground reduces your height and minimizes the risk of a direct strike. It is important to avoid standing in open areas, such as under a tree, as trees can attract lightning strikes. Standing in the doorway of a building is also unsafe as lightning can travel through conductive materials like metal door frames. Going to the highest point in a tall building is dangerous as tall structures are more likely to be struck by lightning. Therefore, the safest options are to get into a metal car or lie flat on the ground in the open to reduce the risk of being struck by lightning.
It is a well-known fact that it takes the Earth approximately 365 days to orbit the Sun. At the same time, the Earth revolves or spins around itself over the course of 24 hours, which explains why we experience day and night. One half of the Earth is always facing the Sun, while the other half is facing away. As a result, different time zones divide the globe. Moving suddenly from one time zone to another, such as when flying from Asia to North America, can cause jet lag. People often feel tired, wake up suddenly during the night, and cannot return to sleep. It takes time to adjust to a new time zone. Another important factor to consider is the slight tilt of the Earth toward the Sun. The Earth does not stand straight but leans slightly to one side. Therefore, when it revolves around the Sun, the middle part of the Earth is always closer to the Sun and receives more heat. This area is called the equator, and the regions above and below it are known as the tropics. Countries located in the tropics receive a consistent amount of daylight throughout the year, with the Sun rising at 6 AM and setting at 6 PM. In contrast, the tips of the Earth, or the poles, receive hardly any light because they are so far from the Sun. There are two main seasons at the poles: 6 months of summer, when the Sun is always shining (even at night), and 6 months of winter, characterized by constant darkness. Between the tropics and the poles lies the temperate zone, where there are four distinct seasons. The Sun rises and sets at different times throughout the year. In spring and summer, it gets light earlier; in fall and winter, it gets dark earlier. People living in temperate zones take advantage of this variation to maximize their daylight exposure. At the beginning of spring, countries in Europe and North America readjust their clocks by moving them an hour ahead. As a result, the Sun does not set around 7 or 8 PM as usual, but an hour later. This practice is called Daylight Savings Time (DST) and lasts until the beginning of fall, when people move their clocks back one hour to Standard or Regular Time. It is believed that Benjamin Franklin first suggested the introduction of Daylight Savings Time in the 18th century, but the first serious proposal came in 1907 from William Willet. However, his idea was shelved by the British government, which deemed it unnecessary. Daylight Savings Time was first implemented by the German government in 1916 in order to save energy during World War I. Shortly after, the United Kingdom followed suit, with the United States doing the same in 1918. The law was unpopular, as people had to wake up earlier, leading many to experience a feeling similar to jet lag. However, the energy crisis of the 1970s forced the U.S. to establish Daylight Savings Time as law. Studies showed that the introduction of Daylight Savings Time in the spring saved the U.S. 10,000 barrels of oil per day between 1974 and 1975. It also prevented 2,000 traffic injuries and 50 traffic-related deaths, saving the country $28 million. Currently, Americans switch to Daylight Savings Time on the first Sunday in April and revert to Standard Time on the last Sunday in October. As of 2007, the time adjustments occur even earlier in March and November.
What does the sentence ‘It takes time to get used to a new time zone’ mean in paragraph 1?
- A. A flight between Asia and North America takes a long time.
- B. Changing time zones makes people feel tired.
- C. People need time to feel comfortable with a new time zone.
- D. It may take weeks to get used to jetlag.
Correct Answer: B
Rationale: The sentence ‘It takes time to get used to a new time zone.’ in paragraph 1 refers to the fact that changing time zones causes jetlag, making people feel tired, waking up suddenly during the night, and having difficulties sleeping. This adjustment period is needed for the body to adapt to the new time zone.