If you are at the zenith of your career, you are ___________.
Correct Answer: C
Rationale: When someone is at the zenith of their career, it means they have reached the highest point or peak of success in their professional life. This suggests that they have achieved their utmost potential and are enjoying the height of their career accomplishments. Choice A, 'just getting started,' is incorrect as it implies the beginning of a career rather than the peak. Choice B, 'preparing for retirement,' is incorrect because being at the zenith of one's career usually signifies the prime of one's professional success, not the preparation for retirement. Choice D, 'having trouble with your superiors,' is incorrect as it is unrelated to the concept of reaching the peak of success in one's career.