1 （is done/ was done）
先来比较被动和主动
somebody built this house in 1961 (主动)
This house was built in 1961 （被动）
主动语态用来说明动作的执行者，
被动语态用来说明动作的承受者，往往不知道或者不必知道动作的执行者，（如果需要知道，则可以用by ）例如
This house was built by my grandfather .
一般现在时
主动 clean(s) /see(s)等
somebody cleans this room every day .
被动 : am /is /are /+ cleaned /seen 等
This room is cleaned every day
Many accidents are caused by careless driving .
一般过去时
主动 ： cleaned / saw 等
Someboy cleaned this room yesterday .
被动 was /were +cleaned /等
This room was cleaned yesterday
