<span>A. The 5 ft plank was too short and needed to be recut. </span>In this sentence, "ft" needs a period at the end so therefore this sentence isn't correctly punctuated. (a is not the answer)
B. Mr. Langan requested a wake-up call for 9:00 a. M. on Saturday. In this sentence, the a.m is punctuated incorrectly so this isn't correct either. (b is not the answer)
C. Why was there such noise at 6:00 AM? Here, it is punctuated correctly. Looks like it is the correct answer.
D. Dr. Vaughn gave Mrs Vaughn a pearl necklace for their tenth anniversary. In this sentence, "Mrs." didn't have a period at the end (d is not the answer).
So the answer was found and it is C because it is punctuated correctly. :)