Miss li asks us to concentrate our attention_____ improve our vocabulary?A in B on C to

问题描述:

Miss li asks us to concentrate our attention_____ improve our vocabulary?A in B on C to
求回答,

concentrate one's attention on [upon]
把注意力集中在
是一个固定搭配
但是这个题目后面是 improve,不是improving,只能用动词不定式to,选C