1. When he arrived at the bus stop, the bus ________ for 20 minutes.

A. has left    B. had left   C. has been away     D. had been away

2、句子中有一些特征词。

     Already  ever  never  just  yet  since….  For…..

     He _____already _____ (see) the film.

     I _______ never ______ (learn)English .

     _______ you ______ (finish) your homework yet?

     The meeting ______ (begin) for two hours.

    动词按其动作发生的方式、发生过程的长短可分为延续性动词与非延续性动词。

    一.延续性动词表示能够延续的动作,如：learn, work, stand, lie, know, walk, keep, have, wait, watch, sing, read, sleep, live, stay等。延续性动词可以与表示时间段的状语连用。

    表示时间段的短语有:for+一段时间,for 2 years; since从句,since he came here; since+时间点名词,since last year, since 5 days ago; how long; for a long time等。

    例:He has lived here for 6 years.  You can keep the book for 5 days. I stayed there for 2 weeks last year.  How long did you stay there last year?

    二.非延续性动词也称终止性动词、瞬间动词,表示不能延续的动作,这种动作发生后立即结束。 如:open, die, close, begin, finish, come, go, move, borrow, lend, buy等。

非延续性动词在肯定句中与表示时间点的状语连用，如：two years ago; at 5 o'clock;

例:He died 5 years ago.

    否定的终止性动词可以与表示时间段的时间状语连用。例:I haven't left here for 3 years. I haven't heard from him for 3 weeks.

三.延续性动词与非延续性动词之间的转换：leave --- be away, borrow --- keep, buy --- have,   begin/start --- be on,   die --- be dead,  finish --- be over,  join --- be in+组织机构, be a member of+组织机构,  open sth --- keep sth open,  fall ill ---  be ill,  get up---be up,   catch a cold --- have a cold,  come here --- be here, go there --- be there,   become --- be,   come back --- be back,  fall asleep --- be asleep,  get to/ arrive/reach --- be (in),  leave --- be away from,  get to know --- know, go (get) out →be out，  put on→ wear；catch a cold →have a cold等。   例:The old man died 4 years ago.  ----The old man has been dead for 4 years.    ---- It is 4 years since the old man died.  ----Four years has passed since the old man died.       He joined the Party 2 years ago.   -----He has been in the Party for 2 years.      I bought the book 5 days ago.  ---- I have had the book for 5 days.

补充练习：

 1、句子中没有明确的时间。

      He _____ (die) last year

      He _____ (die) next week.

      He _____ (die) now.

      He _____ (die)

注：对直线不存在斜率的情形，可不做证明.

因此直线过定点.-------14分

但,这与产生矛盾! ------13分

当时, 直线与椭圆相交于、两点，是关于的方程的两个不相等实数解，从而

当时, ,直线与椭圆不相交于两点，这与直线与椭圆相交于、两点产生矛盾!

将代入椭圆的方程并整理得: ,

若直线不存在斜率，则可设直线的方程为：，