1. when/while/as
e.g. When I came in, he was lying on the bed, staring at the ceiling.（非延；同时）
e.g. He came across a friend when he was walking on the street.（延续；同时）
e.g. When I sat down, I found a silver coin on the ground.（非延；同时）
e.g. The students stopped talking when the teacher came in.（非延；同时）
e.g. I used to go fishing when I lived in the countryside.（延续；同时）
e.g. When they had finished their task, they went out to play.（非延；先）
e.g. He picked up some dialects while he was traveling there.（延续；同时）
e.g. He was knocked down while he was crossing the street.（延续；同时）
e.g. Tom sings as he walks. （一边…一边…）
e.g. As we were going out, it began to rain.（动作几乎同时发生，非常紧凑）
e.g. Just as I patted on her shoulder, she gave out a scream.（动作一先一后但很紧凑）
e.g. As time went on, their hope faded. As spring comes, flowers come out.（随着…）
e.g. We become wiser as we grow older.（随着…）
[Summary]: “when”引导的从句的谓语动词可以是延续性的（此时可以和 “while”互换）也可以是非延续性的，其
动作可以和主句的动作同时发生，也可以先予主句发生。
“while”引导的从句的谓语动词是延续性的，表示主句动作和从句动作同时发生。
“as”表示“一边…一边…”或“随着…”，也可强调两个动作几乎同时发生或一先一后非常紧凑。
[Other functions]:
A. “when”: sb was doing sth when …; sb was going to do sth when …; sb was about to do sth when …
sb was on the point of doing sth when …; sb was ready to do sth when …;
sb had hardly done sth when …; Hardly had sb done sth when …
B. “while”: I am watching TV while she is doing her homework.
C. Also rail travel is very safe and I am never sick on a train, ____ I am on a ship!
A. when B. while C. as D. and
[Exercises]
1. Mother was worried because little Alice was ill, especially ____ Father was away in France.
A. as B. that C. during D. if
2. –I’m going to the post office.
--____you are there, can you get me some stamps?
A. While B. Because C. If D. Since
3. As she ____ the newspaper, Granny ____ asleep.
A. read; was falling B. was reading; fell C. was reading; was falling D. read; fell
4. –Can I join your club, Dad?
--You can when you ____ a bit older.
A. get B. will get C. are getting D. will have got
5. –When will come to see me, Dad?
--I will go to see you when you ____ the training course.
A. will have finished B. will finish C. are finishing D. finish
6. He was about to tell me the secret ____ someone patted him on the shoulder/
A. as B. until C. while D. when
7. Don’t be afraid of asking for help ____ it is needed.
A. unless B. since C. although D. when
8. We were swimming in the lake ____ suddenly the storm started.
A. when B. while C. until D. before
9. Jasmine was holidaying with her family in a wildlife park ____ she was bitten on the leg by a lion.
A. when B. while C. since D. once
10. You can eat food free in my restaurant ____ you like.
A. whatever B. wherever C. whenever D. however
11. He transplanted the little tree to the garden ____ it was the best time for it.
A. where B. when C. that D. until
12. –Did Jack come back early last night?
--Yes. It was not yet eight o’clock ____ he arrived home.
A. before B. when C. that D. until
13. I had just stepped out of the bathroom and was busily drying myself with a towel ____ I heard the steps.
A. while B. when C. since D. after
14. How can you expect to learn anything ____ you never listen?
A. in case B. even if C. unless D. when
15. He was about half way through his meal ____ a familiar voice came to his ears.
A. why B. where C. when D. while
16. –Excuse me. Did you notice whether the No. 108 bus had gone by?
--Not ____ I’ve been standing here.
A. as B. when C. since D. while
17. We were just ____ calling you up ____ you came in.
A. about; when B. on the point of; while C. on the point of; when D. on the point of; as
18. He never thought that his success came ____ he least wanted it.
A. while B. when C. until D. since
19. ____ time going on, his memory of the past faded.
A. As B. When C. With D. While
2. after/before
e.g. The house tumbled down before he rushed out.（来不及…就…）
e.g. The war lasted four years before the North won.（直到…）
e.g. It will be many years before we find cure for AIDS.（之后…）
e.g. I hadn’t waited long before he came.（没…就…）
e.g. Go before I change my mind.（否则）
e.g. I will die before I surrender.（宁可…也不…）
e.g. After I had finished my homework, I went out to play.（可以和 “when”互换）
e.g. I’ll go to see you after I get my hair cut. （可以和 “when”互换）
[Exercises]:
1. ____ three years’ study in this school he entered a famous university and he will graduate ___ two years.
A. In; after B. In; in C. After; after D. After; in
2. He will be back ____ three o’clock.
A. in B. after C. for D. on
3. The doctor will be free ____.
A. ten minutes later B. after ten minutes C. in ten minutes D. ten minutes after
4. He made a mistake, but then he corrected the situation ____ it got worse.
A. until B. when C. before D. as
5. It was evening ____ we reached the little town of Winchester.
A. that B. until C. since D. before
6. Scientists say it may be five or six years ____ it is possible to test this medicine on human patients.
A. since B. after C. before D. when
7. The American Civil War lasted four years ____ the North won in the end.
A. after B. when C. before D. then
8. –How long do you think it will be ____ China sends a manned spaceship t the moon?
--Perhaps two or three years.
A. when B. until C. that D. before
9. –Why didn’t you tell him about the meeting?
--He rushed out of the room ____ I could say a word.
A. before B. until C. when D. after
10. –Why didn’t you help the little boy?
--Oh sorry. He had struggled to his feet ____ I ran over.
A. before B. after C. until D. since
11. When Edison invented the light bulb, he tried over 2000 experiments ____ be got it to work.
A. as B. after C. when D. before
12. “Go out ____ I change my mind!” his father shouted angrily.
A. before B. when C. while D. until
13. Someone called me up in the middle of the night, but he hung up ____ I could answer the phone.
A. as B. since C. until D. before
Question: In exe.4, why not choose “C”?
3. till/until/not until
e.g. I didn’t go to bed until my mother returned.
e.g. I waited until my mother returned.
“until”引导的从句若是和肯定的主句连用，则主句的谓语动词应该是延续性的，表示该动作的结束。 若是和否定的主句连用，则主句的谓语动词应该是非延续性的，表示该动作的开始。 例如：She slept till/until nine. She didn’t sleep till/until nine.
[Exercises]:
1. My uncle ____ until he was forty-five.
A. married B. didn’t marry C. was not married D. would marry
2. –Was his father very strict with him when he was at school?
--Yes. He had never praised him ____ he became one of the top students in the grade.
A. after B. unless C. until D. when
3. They ____ the train until it disappeared in the distance.
A. saw B. watched C. noticed D. observed
4. Mother told Jim to ____ the milk until it boiled and then turn off the gas.
A. observe B. watch C. notice D. glance
5. A good storyteller must be able to hold his audiences’ curiosity ____ he reaches the end of the story.
A. when B. unless C. after D. until
6. Don’t get off the bus until it ____.
A. has stopped B. stopped C. will stop D. shall stop
7. It has been announced that candidates shall remain in their seats until all the papers have been collected.
8. Not until I began to work ____ how much time I’d wasted.
A. didn’t I realize B. did I realize C. I didn’t realize D. I realized
9. It was not ____ she took off her dark glasses ____ I realize she was a famous film star.
A. when; that B. until; that C. until; when D. when; then
10. We were told that we should follow the main road ____ we reached the central railway station.
A. whenever B. until C. while D. wherever
11. “You can’t have this football back ____ you promise not to kick it at my cat again,” the old man said firmly.
A. because B. since C. when D. until
4. since
e.g. It’s years since he smoked.
e.g. It has been many years since I was last in London.
e.g. They have been friends since met in Shanghai.
[Exercises]:
1. It is almost five years ____ we saw each other last time.
A. before B. after C. when D. since
2. –It is weeks since ____.
--So it is. We’d better ask someone else to help us.
A. fell ill B. was ill C. is ill D. has been ill
3. –What was the party like?
--Wonderful. It’s years ____ I enjoyed so much.
A. after B. before C. when D. since
5. immediately/directly/instantly/as soon as
6. by the time
e.g. By the time I arrived, they had gone for a long time.
e.g. By the time the doctor arrived, the patient had died.
[Exercises]:
1. By the time he was twelve, Edison ____ to make a living by himself.
A. would begin B. has begun C. had begun D. was begun
7. the moment/the instant/the minute/the first time/the last time
e.g. We became friends the first time we met each other.
e.g. It is the first time I have been here.
e.g. It was the first time I had been here.
e.g. It will be the first time I have been here.
[Exercises]:
1. –Do you know our town at all?
--No. This is the first time I ____ here.
A. was B. have been C. came D. am coming
2. I thought her nice and honest ____ I met her.
A. first time B. for the first time C. the first time D. by the first time
8. “as long as”
e.g. You can stay here as long as you like.
e.g. You can keep this book as long as you like.
e.g. As long as it doesn’t keep me awake at night, I don’t see any harm in drinking tea.
9. “once”
[Exercises]: The research is so designed that once ____ nothing can be done to change it.
A. begins B. having begun C. beginning D. begun 123