Answer:
B. fluid ounce
Explanation:
Just do this as a process of elimination if you're not sure. A glass isn't very big, so gallons wouldn't be the most appropriate. Same thing for kilograms. Inches could work quite well, but fluid ounces are even better as they specifically measure liquids, therefore why it would be the most appropriate.
However, keep in mind that they could all be used to measure liquids/volumes.