they spent as many hours as they could (to study)their lessons?

问题描述:

they spent as many hours as they could (to study)their lessons?
这个地方用到什么语法?

定语从句吧
省略了that
定语从句修饰代词they
本来这句话是完整的
而从句又有它独立的主谓宾
所以是由That引导的定语从句