牛津高中英語語法復習：動詞時態

　 注意：非延續性動詞的否定形式可以與表示延續時間的狀語連用。即動作不發生的狀態是可以持續的。
（錯）i have received his letter for a month.
（對）i haven't received his letter for almost a month.
12 比較since和for
　　since 用來說明動作起始時間，for用來說明動作延續時間長度。
　　i have lived here for more than twenty years.
　　i have lived here since i was born..
　　my aunt has worked in a clinic since 1949.　
　　some new oilfields have been opened up since 1976.
　　i have known xiao li since she was a little girl.　
　　my brother has been in the youth league for two years.　
　　i have not heard from my uncle for a long time.
    注意：并非有for 作為時間狀語的句子都用現在完成時。
　　 i worked here for more than twenty years.
　　　(我現在已不在這里工作。)
　　 i have worked here for many years.　　　
　　　(現在我仍在這里工作。)
    小竅門：　當現在完成時+一段時間，這一結構中，我們用下面的公式轉化，很容易就能排除非延續動詞在完成時中的誤使。
　　1)　(對) tom has studied russian for three years.
　　　 = tom began to study russian three years ago, and is still studying it now.
　　2)　(錯) harry has got married for six years.
　　　 = harry began to get married six years ago, and is still getting married now.
　　顯然，第二句不對，它應改為 harry got married six years ago.　或 harry has been married for six years.
13 since的四種用法
　 1) since +過去一個時間點　(如具體的年、月、日期、鐘點、1980, last month, half past six)。
　 i have been here since 1989.
　 2) since +一段時間+ ago
　 i have been here since five months ago.
   3) since +從句　
　 great changes have taken place since you left.
　 considerable time has elapsed since we have been here.
   4) it is +一段時間+ since從句
　 it is two years since i became a postgraduate student.
14 延續動詞與瞬間動詞
1) 用于完成時的區別
　　延續動詞表示經驗、經歷； 瞬間動詞表示行為的結 果，不能與表示段的時間狀語連用。
　　 he has completed the work.　　他已完成了那項工作。 (表結果)
　　 i've known him since then.　　 我從那時起就認識他了。(表經歷)
2)　用于till / until從句的差異
　　 延續動詞用于肯定句，表示"做……直到……" 瞬間動詞用于否定句，表示"到 ……，才……"
　　 he didn't come back until ten o'clock.
　　　　他到10 點才回來。
　　 he slept until ten o'clock.　　　　　
　　　　他一直睡到10點。
　典型例題
1. you don't need to describe her. i ___ her several times.　
a. had met　b. have met　 c. met　d. meet
　 答案b. 首先本題后句強調對現在的影響，我知道她的模樣，你不用描述。再次，several times告知為反復發生的動作，因此用現在完成時。