for與since 的辨析
for后須接“時(shí)間段”,since后須接“時(shí)間點(diǎn)”,二者可以轉(zhuǎn)換,均須與延續(xù)性動(dòng)詞連用,也可以與非延續(xù)性動(dòng)詞的否定式連用。二者引出的時(shí)間狀語往往用 how long提問。
for;since
for與since都能與現(xiàn)在完成時(shí)連用,但區(qū)別較大:
for后須接“時(shí)間段”,since后須接“時(shí)間點(diǎn)”,二者可以轉(zhuǎn)換,均須與延續(xù)性動(dòng)詞連用,也可以與非延續(xù)性動(dòng)詞的否定式連用。二者引出的時(shí)間狀語往往用 how long提問。如:
he has been here for two years.=he has been here since two years ago.他來這里已有兩年了。
—how long have you had this book?這本書你買多久了?
—for a week./since a week ago.買一周了。
we haven't heard from him for a month.我們已有一個(gè)月沒收到他的來信了。
since能引導(dǎo)時(shí)間狀語從句(主句用現(xiàn)在完成時(shí),從句用一般過去時(shí)),而for則不能。如:
he has taught here since he came to china.自從他來到中國就在這兒教書。 it is /has been an hour since he left here.他離開這兒已有一小時(shí)了。
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