I encourage you to flip through your textbooks(if you have one) and review what you learned.
I believe the answer is D.
Process of elimination: For C, you don't quote a number in a sentence.
For B, I believe you don't ever use "s's." (Mind my
quotation mark use please)
For A, I think, I repeat, I T-H-I-N-K, that you put
quotation marks around "an."
Possible answers are A or D. Up to you, I can't help you do your homework.
