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I have worked here since 2002.
自从2002年以来我就在这儿工作。
They have learned English for three years.
他们学英语3年了。
注意：1）since + 点时间， for + 段时间， 如：since last week, for two days。
2. 短暂性动词(come, go, leave, buy …)可以用于现在完成时。但不能用于带有
for或是since的肯定句中。
He has left Beijing for a week.
He has not left Beijing yet.
(×)
(√)
3. 短暂性动词变为延续性动词的现在完成时构成举例：
buy have / has had
borrow have / has kept
arrive/reach/get to-- have / has been in /
at
leave have / has been away
open have / has been open
join have / has been in
have / has been a member of
die have / has been dead
marry have / has been married
come / go have / has been in / at
begin / start have / has been on
finish / stop have / has been over
fall asleep have / has been asleep
get up have/has been up
become have/has been
The old man died two years ago.
这个老人两年前死了。