You can (and it'll be to your benefit to) use big words if you're sure of their meanings. If you try to use big words you're not sure of, you run the chance of misusing the words and you can lose points. I'd like to give you some more tips, but I'm just as confused myself... about essay structuring.
When one <first begins> to play tennis, <it’s>
(A) (B)
important to work on <your> serve, and to wield
(C)
your racket <well> . No error
(D) (E)
Spark Notes says that the answer is C because the pronoun "your" does not agree with "one" in the original. I know its not a choice, but isnt "your" in "your racket" incorrect for the same reason?