They made full use of the time they could ___ to do experiment.填spare.只知道spare time to do,求解释这里spare to do 是什么用法.
问题描述：
They made full use of the time they could ___ to do experiment.
填spare.
只知道spare time to do,求解释这里spare to do 是什么用法.
答
1）be to do: (1)表示事先商定、安排或准备要做的事情。如： The I felt nervous because I was soon to leave home for the first time.
答
they could spare应该是定语从句修饰the time,
后面的不定式应该是use的用法,use sth to do