Which sentence correctly forms the plural of the letter x?

AHow many xs are in exaggerate?
BHow many x's are in exaggerate?<=my ans.
CHow many xs' are in exaggerate?

Verified Answer :

The correct answer for the question that is being presented above is this one: "b. How many x's are in exaggerate?" The sentence that correctly forms the plural of the letter x is this b. How many x's are in exaggerate?. The reason for that is because of a rule for single-letter plural.