延续性与非延续性动词在现在完成时态中的使用
☆有一些动词是瞬间动词，也叫非延续性动词，这些动词一发生就结束了，常见的有：come, go, arrive, reach, leave,begin, start, buy, join, die, borrow, get up, become, open, stop等。

这些动词虽然可以用于现在完成时（说明某个动作的结果还存在），但由于它们不能延续，因此不能跟表示一段的时间状语连用。

e.g. Jim has come back. (正)
Jim has come back for a month. (误) come back的动作不能延续一个月，因此错误。

☆瞬间动词不可以用于有段时间的现在完成时态中，因此，若要解决这一问题，就应把它改为相应的延续性动词或短语，主要有以下几种：
①用相应的延续性动词
如：buy →have borrow →keep come/go/become →be
put on →wear catch a cold →have a cold
②转换成be+名词
如：join →be a member of go to school →be a student
③转换成be+形容词或副词
如： die →be dead leave →be away begin →be on finish →be over fall asleep —be asleep open →be open get up →be up close →be closed
④转换成be+介词短语
如： come to/go to/arrive in (at)/get to/reach …→be in/at… join the army →be in the army(军队)
e.g. I have borrowed the book. I have kept the book for two days.
Jim has joined the band. Jim has been a member of the band for a month.
His grandfather has died. His grandfather has been dead for 2 years.
My father has arrived in China. My father has been in China for a week.
☆在否定句中，非延续性动词也可以与时间段连用。

e.g. I haven’t borrowed books from the library since last year. 自去年以来我就没有在图书馆借过书。

Jim hasn’t come back for a year. 吉姆已有一年没回来了。

☆现在完成时的几种常见的句型转换。

现在完成时可以转化成一般过去时，还可以转化成“It is/has been +时间段+since从句(用一般过去时)”等句型。

e.g. Jim has been back for a month.
= Jim came back a month ago.
= It is/has been a month since Jim came back.
= A month has passed since Jim came back.
I have kept the book for two days.
= I borrowed the book two days ago.
= It is / has been two days since I borrowed the book.
= Two days has passed since I borrowed the book.。