five pieces of cake /five pieces of cakes哪个才对?

题目

five pieces of cake /five pieces of cakes哪个才对?
--What would you like,sir?
--I'd like____________.
A.two glass of milk and five piece of cakes
B.two glasses of milk and threes of cake
C.four glasses of milk and five pieces of cakes
D.four glass of milk and five piece of cakes
为什么选C?

答案

C.four glasses of milk and five pieces of cakesfour glass is wrong- 4 need a plural therefore you need to add ES to Glass...all the rest are wrongb- threes of cakes..but threes WHAT?