C.完成时态使用注意事项
① 完成时的时间状语一般表示到为止,以by短语居多。如果句中的时间状语是由by引出的短语或从句,谓语动词一般是用完成时态,如:
By the time we got there, the fire had already been put out.
Well have completed the task by the time you come back.
② 在完成时态中,终止性动词不能与表示一段时间的时间状语连用,而表示状态或动作持续的谓语动词必须与表示一段时间的状语连用。
The conference ____ a full week by the time it ends
A. must have lasted
B. will have lasted
C. would last
D. has lasted
It seems oil ___ form this pipe for some time. Well have to take the machine apart to put it right.
A. had leaked
B. is leaking
C. leaked
D. has been leaking
这两题中都有表示动作持续的一段时间,应该用完成时态。
但是,如果只表示状态已经存在,则不能用完成时态,如:
By then, he knew what he waned to be when he grew up.
③ 完成时可以用来表示量的积累。
④ 对于完成时的考查有两种,一种是时态本身的选择,另一种是根据时态选择时间状语,如6)。从句时态为过去完成时,表示等到他回来,客人都已经离开了,与完成时态连用的,表示到为止的应该是介词by。
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