What Is the AP Standard for the Use of Apostrophes

Multiple Choice

What is the AP standard for the use of apostrophes with numbers and individual letters?

A) Always use apostrophes with both except with the letter A.
B) Do not use apostrophes with either except with the letter A.
C) Always use apostrophes with numbers but never with individual letters.
D) Always use apostrophes with individual letters but never with numbers.