关注. had done是过去完成时，如果动作发生在相对于过去某一时刻的过去，在过去某时刻已经完成了，就用had done。. have/has done是现在完成时，是相对于 …
Could have, would have, and should have are sometimes called “modals of lost opportunities”. Both your sentences are incorrect (never use has or had to form …
说明白点，have done 是过去完成，had done 是过去的过去完成。 3.举例子： 现在完成时是描述过去发生的而与现在情况有关的事或状态（例2），或是从过去某时 …
A past perfect like had done, however, must be related to a past Reference Time: it distinguishes an event as having taken place “before then”, not “before now”. …
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