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.

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.

It is to look

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