语态：主动语态：表示主语是动作的执行者
被动语态：表示主语是动作的承受者
一般现在时的被动语态：助动词is/am/are+P.P.(过去分词）
The Olympic Games is held once ever four years.
一般过去时的被动语态：助动词was/were+P.P.
The bridge was built in 1995.
一般将来时的被动语态：助动词will+be+P.P.
The teaching building will be put up next year.
过去将来时的被动语态：助动词would+be+P.P.
现在进行时的被动语态；助动词is/am/are+being+P.P.
A new factory is being built in our town.
现在完成时的被动语态：助动词have/has+been+P.P.
He has been sent to work in Tibet.
情态动词的被动语态；情态动词+be+P.P.
Your homework must be finished as soon as possible.
Teenager should not be allowed watch TV every night.
过去进行时的被动语态：助动词was/were+being+P.P.
When I got home ,dinner was being cooked by mother.