現在完成時
可以表示動作或狀態從過去某時間一直持續到現在，可能剛剛結束，也可能繼續下去.
常與for或 since表示一段時間得時間狀語連用。
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辨析: since，for, from
for 和since 所引導得時間狀語都表示一段時間。
for +一段時間 ：表示動作持續多長時間
since + 時間點：表示動作是什么時候開始得
對劃線部分提問都用How long
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1.for 介詞，長達，后接時間段,for+一段時間，所指一段時間不明確，表示動作持續多長時間，要用延續性動詞
for a year for two weeks for three years
I haven’t seen her for two days.
I have been living here for 10 years.
He has kept the book for 2 weeks.
I have been here for 5 weeks.
He’s studied English for 3 years.
We haven't seen him for two years.我們已經兩年沒見他了。
I have studied English for two years.我學英語已經兩年了。
2.for+時間段 可以使用不同得時態。
I stayed in the hotel for a week last summer. 一般過去
I have stayed in the hotel for a week. 現在完成
I will stay in the hotel for a week next month.一般將來
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for a time一小段時間;一度;一時
for后接表示時間段得名詞短語
We lived in Hangzhou for a time.我們在杭州住過一段時間。
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from后接具體時間，說明從什么時候開始，不說明某動作或情況持續多久。
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1.I'm looking after Tom today. He’s been in house 8:00 this morning.
A. at B.since C. for D.till
