It was repairing the old clock that the old man spent the whole morning at home.

题目

It was repairing the old clock that the old man spent the whole morning at home.
为什么用REPARING

答案

it指代的是the old man spent the whole morning at home.
所以题目变为 The old man spent the whole
morning ( ) the old clock at home.
spend (on) doing sth
所以：REPARING