Answer:
I would choose letter C instead of letter A.
C. again under James Madison, becoming one of only
Explanation:
We must choose the best way to complete the sentence:
George Clinton, the governor of New York for many years, served as Vice President under Thomas Jefferson, and________________________two men to serve as Vice-President under two different US Presidents.
First, there is no need to repeat the subject or the verb. We know the sentence keeps on talking about the same topic, George Clinton. And, since we are about to mention the two presidents he served as Vice President under, we don't need to use the verb "served" again. Once is enough to include both times. Also, we must be careful where we place the word "only", since it can change the meaning of the sentence. If we say he became "only one" of two men, it sounds as if we are diminishing his importance. If we say the became one of "only two men", we are doing the opposite. There were only two men to serve as Vice President under two different US Presidents. Being one of them is a great deal. That's why I believe letter C to be the best choice:
George Clinton, the governor of New York for many years, served as Vice President under Thomas Jefferson, and again under James Madison, becoming one of only two men to serve as Vice-President under two different US Presidents.
