What are the trees used___?
问题描述:
What are the trees used___?
They can be used ___ make paper and pencils.
A for,to B to,as C on ,to
答
A
be used for 被用来...
be used to do 被用来做...
这些树被用来做什么?
它们被用来制作纸张和铅笔.