不是祈使句,是一个句子的缩写：The mission has been completed或The mission is completed. 再问： 只有主语吗？ 再答： The mission has been completed 主语：The mission 谓语：has been completed The mission is completed. 可以看成被动语态： 主语：The mission 谓语：is completed 也可以看成主系表结构： 主语：The mission 系动词：is 表语：completed
