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