Discuss waht they were made of and explain their use.
问题描述：
Discuss waht they were made of and explain their use.
可以说一下这里的use 为什么不用复数吗?they不是有复数的意思吗?
答
use 当“用处”讲的时候是不可数名词.这句话意思是：讨论一下它们是用什么做的并解释它们的用处.