它们是be动词的过去式。
作助动词：
现在分词，构成过去进行时态：
He was reading.
过去分词，构成被动语态：
They were defeated.
扩展资料
作系动词：
现在分词、动名词短语作表语：
The film was moving.
His job was teaching English .
过去分词作表语：
We were moved.
不定式作表语：
1）有to不定式：His work that day was to clean the blackboard.
2) 无to 不定式：What he should do is clean the blackboard.
