What is the word part placed before a word to change its meaning?
Correct Answer: A
Rationale: A prefix is the correct answer. A prefix is a word part attached at the beginning of a word to modify its root word, changing the definition or grammatical function of the word. Examples of prefixes include "un-" in "unhappy," "re-" in "redo," and "pre-" in "preview." Choice B, "Affix," is incorrect because while a prefix is a type of affix, not all affixes are prefixes. Choice C, "Suffix," is incorrect as a suffix is a word part added at the end of a word to change its meaning. Choice D, "Vocab," is incorrect as it refers to vocabulary or words related to a particular subject rather than a word part placed before a word.