In which sentence are all periods used correctly?
A. Mr. Langan requested a wake-up call for 9:00 A.M. on Saturday.
B. Dr. Vaughn gave Mrs Vaughn a pearl necklace for their tenth anniversary.
C. The 5 ft plank was too short and needed to be recut.
D. Why was there such noise at 6:00 AM?
Letter A! The "A.M." Is (obviously) a time (morning!) fun fact A.M. Stands for ante meridiem (ante is Latin for before and meridiem is Latin for middle) :)