问题描述：
It's very polite( )you to help others when they need help.
A.of B.for C.with D.on
书上答案是A,但有一个句式是It's+a.+for sb.+to do sth.,为什么不是B呢?
A.of B.for C.with D.on
书上答案是A,但有一个句式是It's+a.+for sb.+to do sth.,为什么不是B呢?
问题解答：
我来补答展开全文阅读