作系動詞：

　　現在分詞、動名詞短語作表語：

　　The film was moving.

　　His job was teaching English .

　　過去分詞作表語：

　　We were moved.

　　不定式作表語：

　　1）有to不定式：His work that day was to clean the blackboard.

　　2) 無to 不定式：What he should do is clean the blackboard.