Question

The window____ a moment ago.No one knew who had done it.

Answer 1

三者时态不同,分别为过去完成时,现在完成时,一般时.

为了帮助你理解,举几个例子：

1.He told me that the book had be stolen by John.

2.John has stolen the book.=The book has been stolen by John.

3.Book is lost.

另外had been done 可以用于虚拟语气如：

if I had stolen the book ,how can I be present?

had been done 表过去的过去has been done 表过去对现在的影响 be done 若为were/was done 表示一般过去 若为is/are/am 表现在

还有何疑问?很乐意为你解答.同意请采纳.天天向上.