Question

I'm not sure how many ____ of water I'm supposed to drink every day.

A: Cups
B: Cup's
C: Cups'

Answer 1

The answer is A. cups

B would be if you are talking about something that the cup owns, or something that is a part of the cup... for example: The cup's handle is blue.

C would be talking about something that belongs to multiple cups... for example: All of the cups' handles are blue.

Answer 2

The answer is A. Cups. Cups isn’t possessive, like the other answers are, and the statement isn’t saying that the cups of water belong to anyone, so the answer isn’t supposed to be possessive, just plural. So the answer is A.