To look after the sick boy is my duty为什么要用to?

分类: 作业答案 • 2021-12-28 17:45:18

问题描述：

To look after the sick boy is my duty为什么要用to?
此句的同义句填空：——my duty —— ——after the sick boy.

答

不定式短语做句子的主语.
It's my duty to look after the sick boy.