辨析before和since

辨析before和since
先看下面两道试题：
1、What was the party like?
Wonderful .It’s years I enjoyed myself so much. (NMET93)
A.after
B.before
C.when
D.since
2、She was so interested in the book that she had read it for three bours she realized it.
A.when
B.sunce
C.before
D.until
在1题中，上下文提供人语言环境是：说话个方想询问另一方对晚会飞感受，另一方表达的一丝丝“晚会很精彩，自我上次玩得很开心以来已有好几年了。

”，时间的计算式从since从句飞完成或状态结束时算起。

因此应该选择D。

在2题中，上下文透露的语言信息是：在她意识到时间问题之前，时间已不知不觉飞过了三个小时。

也就是说三小时之后从句中的动作才开始。

答案应该选择C。

一、若表示“还未……就……”“不到……就……”“……才……”，“趁……还没来得及”是，需用连词before,此时从句中的谓语动词不能用否定时。

如We had sailed four days and four nights before we saw land.我们航行了四天四夜才看到陆地。

We hadn’t run a mile he felt tired.我们没跑到一英里，他就累了。

Please write it down before you get in a word, had measued me.我还没来得及插话，他就给我量好了尺寸。

Before they reached the station, the train had gone.他们(还没)到火车站之前，火车已开走了。

二、在“It+be+一段时间十before从句”句型中，如果主句为一般将来时，从句常用一般现在时；如果主句为一般过去时，从句则常用一般过去时。

如：
1、It will be six years before we again.
A.will meet
B.meet
C.met
D.have met (答案为B)
2、It not long before he told us about the af-fair.
A.will be
B.is
C.had been
D.was (答案为D)
除此以外，“It will be + before sb. does”还表示“多久之后才……”。

如：It will be half a year before I come back.我半年后才回来。

It won’t be long before we meet again.不久，我们又会见面的。

三、在“It+be+一段时间+since从句”句型中，如果主句为一般现在时或现在完成时，从句常用一般过去时；如果主句为一般过去时，从句则常用过去完成时。

如：They asked me to have a drink with them. I said it was at least ten years since I a good drink. (MET’88)
A.had enjoyed
B.was enjoying
C.enjoyed
D.had been enjoying (答案为A)
四、在“It is+时间+since从句”句型中，时间的计算根据since从句中的谓语动词的情况进行推算，瞬间动词(如：break out,join,cach等)是从动作发生时算起，延续行动词，(如：smoke,work,live,have等)是从动作结束时算起。

如：It is three years since the War broke our. (从break out 动作发生时算起)战争爆发以来，有三年了。

It is three years since she was in our class.她离开我们班哟三年了。

It is five years since I (have)smoked a cigar.(=since I stopped smoking a cigar.) (从smoke动作结束时算起)我不吸烟有五年了。

如果译成“我不吸烟有五年了”，应为：It is five years since I began to smoke.
五、综合练习
1、The next moment, she had time to realize what was happening,she was hit over the head.
A.when
B.before
C.since
D.as
2、—Why didn’t you try your best to get on the bus?
—I tried to,but I could,it started moving.
A.until
B.when
C.before
D.after
3、Mr.Smith is in good health now for it is quite a long time he smoked.
A.until
B.since
C.before
D.when
4、—It is a long time I saw you last.
—Yes, and what a pity is since it will be a long time we see each
other again.
A.before,since
B.since,before
C.when,when
D.since,when
5、We drove abroue about 200 kilometers we got to the town.
A.before
B.since
C.until
D.while
6、It’s ten years the scientist set out start his work of discovery the valuable chemical.
A.before
B.that
C.since
D.when
7、A man escaped from the prison last might. It was a long time the guards discovered what had hap-pened.
A.before
B.until
C.since
D.when
(答案：1、B 2、C 3、B 4、B 5、A 6、C 7、A)。