When their father died,they thought it their duty to keep Eric in hiding.

题目

When their father died,they thought it their duty to keep Eric in hiding.
it后面是不是省略了be动词,如果是,为什么可以省略呢,如果不是,it后面怎么可以直接加their...

答案

think it + noun/adj+for sb + to do sth
their duty is a noun