a．When the subject is the doer of the action，the verb is in active voice．

当主语是动作的施动者时，动词用主动态。

The auditor signed the reports．

Miss Pulaski sent Joyce a copy of the invoice．

The owners must make the necessary repairs．

b．When the subject is not the doer of the action，the verb is in passive voice．A verb in passive voice always includes a form of the verb be(am，is，are，was，were，be，been，being)as a helping verb，and the main verb is always a past participle．

当主语是受动者，则须用被动语态，动词的被动语态一般由系动词加过去分词构成。

The reports were signed by the auditor．

Joyce was sent a copy of the invoice by Miss Pulaski．

A copy of the invoice was sent to Joyce by Miss Pulaski．

The necessary repairs must be made by the owner．