被动语态：
have/has been+done：现在完成时的被动语态,对现在造成一定影响,
etc．：the preparations for the task has been done,we can get down to it now
had been+done,过去完成式的被动语态,对过去造成一定影响,
being+done,现在进行时的被动语态
is/are+done,一般现在时的被动语态
was/were+done过去时的被动语态
原句:they canceled all flights because of fog
答案为什麽是:all frights were canceled.而不是;all flights have been canceled.
因为原句就是过去时态,主语＋动词的过去时,所以变换句型时,也要相应的用过去时,
原句:they are buliding a new shopping center downtown.
答案为什麽是:A new shopping center is being bult.
在这裏为什麽要用being..
原句用的就是进行时态
Linda didn't have her car yesterday(it/tune-up/at the garage)
答案为什麽是:it was being tuned-up at the garage..这裏怎麽会用being的..
他昨天没有开车是因为它的车正在被维修,
你可以把英语先译成汉语,再熟悉的语境中找感觉,习惯了就会用了
注：在句型转换中,一定要保持事态的对应
即：现在完成式——现在完成式
一般现在时—— 一般现在时
一般过去时—— 一般过去时
现在／过去进行时——现在／过去进行时
被动语态类推,
了解语境
不懂再问