补语(complement): 补语用于说明主语或宾语。分别称为宾语补足语和主语补足语。补语例句如下：
He thinks the girl beautiful.
The doctor advised her to have a good rest.
You should get on the plane in turn.
若动词宾语较长，通常用it做形式宾语代替其位置，而将其移至宾语补足语之后：
I found it difficult to finish the task in time.
We have made it clear that we disagreed.
主语补足语：含宾语补足语的句子在转换成被动语态后，原有的宾语和宾语补足语就变为主语和主语补足语。
We found him working in the office. He was found working in the office.