We thought it our duty to take care of the orphans.

问题描述:

We thought it our duty to take care of the orphans.
为什么不用“We thought it is our duty”呢?

如果用it is our duty,那么这个句子就变成了宾语从句,是复合句;但是如果去掉is,那么our duty就作为宾语补足语,整个句子就成了简单句.