辨析: since，for, from
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表示一段時間的時間狀語連用。
for +一段時間 ：表示動作持續多長時間
since + 時間點：表示動作是什麼時候開始的
1.for 後接時間段，常用於完成時，句中要用延續性動詞；
2.since “自從”，後面接時間點或一般過去時的句子或時間段+ago。前面的謂語動詞或主句的謂語動詞必須用完成時態，要用延續性動詞。
She has lived here for ten years。
=She has lived here since ten years ago。 她已經在這裡住了十年了。
1.for 介詞，長達，後接時間段,for+一段時間，所指一段時間不明確，表示動作持續多長時間
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 可以使用不同的時態。
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
for a time一小段時間;一度;一時
for後接表示時間段的名詞短語
We lived in Hangzhou for a time。我們在杭州住過一段時間。
1.
since自從，自從…以來 +時間點或從句
表示動作是什麼時候開始的
①since+時間點 介詞
since last week since 2009
I have been here since 2009.
He has stayed here since 5 o’clock.
I have been living here since 2000.
I haven’t heard from him since last summer.
I got a headache since last night.我從昨晚開始就一直頭痛。
They have lived in Beijing since 1980.他們自1980年就一直住在北京。
②since+ 時間段+ ago since 5 hours ago
He has stayed here since 5 hours ago.
③since+ 一般過去時的時間狀語從句 連詞
I haven’t seen him since I left that factory.我自從離開那家工廠還沒見過他
We’ve known each other since we were children.我們從小就認識。
I have been here since I graduated in 2000.
She has taught English since he came here.
since+過去的時間點
=since+一般過去時的句子
=for+時間段
I have lived here since two years ago.
=I have lived here for two years.我住在這兒兩年了
I’ve lived here for 15 years.
=I’ve lived here since 15 years ago.
I have been here for 5 years.
=I have been here since 5 years ago.
2.既然；因為
Since you agree with me, let’s start together.既然你同意我的觀點，讓我們一起開始吧。
3.since 也可單獨使用, 自那時起; since前也可加上ever,加強語氣.
I have been here (ever) since.
I have been here (ever) since I graduated in 2000.
It is +一段時間+since+句子(一般過去時)
= 一段時間+has passed +since + 句子(一般過去時)
It is five years since I joined the army.
=Five years has passed since I joined the army.
since then從那以後，句子常用現在完成時，且句中的動詞應用延續性動詞，如果為非延續性動詞必須把它轉換為延續性動詞。
He has written more than 10 books since then。從那以後他寫了十多本書
I haven‘t heard from her since then。從那以後，我沒有收到地的來信。
We have been good friends since then。從那時起我們就成為好朋友。
from後接具體時間，說明從什麼時候開始，不說明某動作或情況持續多久。
I'm looking after Tom today. He’s been in house 8:00 this morning.
A. at B.since C. for D.till
B