[析] while不能表达一点儿的时间，即瞬时某一时间点。

　　[误] After school some students play football, or others go to the library.

　　[正] After school some students play football, while others go to the library.

　　[析] while在此处意为"而，然而"。

　　[误] She sang when she walked along the dark street.

　　[正] She sang as she walked along the dark street.

　　[析] as用于句中时，其要点是强调两个动作的同时进行。这里用when虽然不能讲是语法上的错误，但则看不出来小女孩因独自走黑暗的街道因害怕而唱歌的心情。

　　[误] I finished my homework until twelve o'clock last night.

　　[正] I didn't finished my homework until twelve o'clock last night.

　　[正] I did my homework until twelve o'clock last night.

　　[析] until用在句中时其含义是某一动作一直持续到某时结束，那么句中的动词则一定要用持续性动词，如果要用瞬间，或截止性动词时一定要用否定句式。因截止 性动作的否定式应看作是持续性的动作。如离开leave是瞬间动作，因一出门即为离开了，而不离开则是长时间的。

　　[误] I have studied English when I was twelve.

　　[正] I have studied English since I was twelve.

　　[析] since引出的时间状语从句是表达了一个时间点，而这个时间点是主句动作的启始点，所以主句一般要用完成时态。

　　[误] Because he didn't study hard, so he didn't pass the exam.

　　[正] He didn't pass the exam because he didn't study hard.

　　[析] because 与 so在英文中两者不能并用的，只能在句中用其一。

　　[误] He was such excited that he could not speak.

　　[正] He was so excited that he could not speak.

　　[析] so与such的用法可以分为四种情况，①用于单数可数名词之前，其格式是such+不定冠词+形容词+单数可数名词，如：It is such a beautiful book that every child likes it. 也可以用so, 其格式是so+形容词+不定冠词+单数可数名词，如：It was so beautiful a book that every child likes it. ②在不可数名词前或可数名词复数前这时只能用such, 如：It is such good weather that we want to swim. 又如：They are such good students that they can pass the exam easily. ③在few, little， much, many 这4个字前只能用so而不能用such, 如：I have so much money that I can buy everything I want. ④当that前只有形容词或副词时，这时只能用so, 如：She is so beautiful that every one likes her. He ran so fast that I couldn't keep up with him.

　　[误] He got up earlier this morning so as to that he could catch the first bus.

　　[正] He got up earlier this morning so as to catch the first bus.

　　[正] He got up so earlier that he could catch the first bus.

　　[析] so…that与so that的用法有相同之处，那就是其后接从句，而so as to 其后要接不定式，即动词原形。这样的词组还有：in order to。

　　[误] I want to buy same stamp that you have.

　　[正] I want to buy the same stamp as you have.

　　[析] the same…as (that)这是个固定用法，在same前的定冠词是不能少的。而the same…that意为"我要的就是那一个"。而the same…as为"要的是和……一样的东西"。

　　[误] Before I do not give you the answer, I'll ask you some questions.

　　[正] Before I give you the answer, I'll ask you some questions.

　　[析] 这种错误是由于受中文的影响。在中文中可以讲"我没给你答案前"。而英文用了before就不要再用否定句了。

　　(三) 例题解析

　　1? We bought Granny a present, ___ she didn't like it.?

　　A. but B. and

　　C. or D. so

　　[答案] A.

　　[析] 由于句意的原因，应选择转折连词。

　　2? Run quickly, ___ we'll miss the early train.?

　　A. and B. but

　　C. so D. or

　　[答案] D.

　　[析] or这里应译为：否则。

　　3? I'll give the book to him ___ he comes back.?

　　A. since B. as soon as

　　C. before D. until

　　[答案] B.

　　[析] as soon as 引出的时间状语从句应用一般现在时表示将来要发生的动作。

　　4? Don't cross the road ___ the light turns green.?

　　A. when B. while

　　C. until D. as

　　[答案] C.

　　[析] until应译为"直到……才"，因为前面的祈使句为否定句。又如：She did not go to bed until her mother came back. 应译为"直到她妈妈回来她才睡觉"。

　　5? Miss Gao has been a teacher ___ 1990.?

　　A. before B. after

　　C. since D. in

　　[答案] C.

　　[析] 因为主句为完成时，所以应用 since表示该动作的启始点。

　　6? - Which would you like better, tea ___ milk??

　　- Tea, please.?

　　A. but B. and

　　C. or D. with

　　[答案] C.

　　[析] 在疑问句与否定句中应用or来表示一种选择。

　　7? We love spring ___ there's beautiful flowers every wher.?

　　A. though B. but

　　C. or D. because

　　[答案] D.

　　[析] 因为这里表示的是因果关系。

　　8? Please leave ___ 7∶00, then you'll be able to get ___ there earlier.?

　　A. till, in B. from, /

　　C. before, / D. behind, to

　　[答案] C.

　　[析] before为在7∶00之前离开。

　　9? The teacher didn't begin the lesson ___ all the students stopped talking.?

　　A. until B. after

　　C. if D. because

　　[答案] A.

　　[析] 这句应译为"直到所有的学生都停止讲话老师才开始上课"。因begin为瞬间动词，所以应用否定句。

　　10? Betty didn't go to see the film yesterday ___ she was ill.?

　　A. but B. until

　　C. if D. because

　　[答案] D.

　　[析] 这里是表示因果关系，所以应用because。因为她病了所以未去看电影。