A. Useful expressions
1. for a while 一会儿， 它可用于一般时，过去时，将来时，完成时，常与持续性动词连用。
We talked with each other for a while.
I haven’t heard from him for quite a while.( for quite a while=for a long time)
Cf: after a while 过一会， 一会儿后， 常与终止性动词的一般过去时连用。
After a while they started out.
2. cut off ----- shut off（电路）切断，停（水，电）
The electricity was cut off for several days.
3. stay up -----not fall down ,not go to bed
I stayed up until Father came back.
4. for ever (AE forever)终身
We’ll remember him for ever.
5. a (large/great)number of., a great many许多与复数名词或代词连用
I have a number of letters to write.
There are a large number of places to visit in Beijing.
A great many words and expressions have come into the language from American English.
Cf: the number of 是……的数量，谓语动词常用单数
The number of pages in this book is 500 hundred.
6. time 作“倍数”解，是可数名词，如 three times four times ，但两倍要用 twice
1)表示甲比已乙大（高，长，宽等）几倍的句型是：
A is three( four etc.) times larger/bigger(higher, longer, wider,etc.) than B.
Their school is three times larger than ours.
2) 表示甲是乙的几倍大（高，长，宽等）的句型是：
A is three (four,etc. )times as big (high ,long,wide,etc.)as B.
Asia is four times as large as Europe.
当然这两个句型可以互换但要注意准确性。
This street is three times longer than that one.
This street is four times as long as that one.
7. afraid 的几种用法。
1)be afraid of sth. 害怕……
The little girl is afraid of dogs.
2)be afraid to do sth. 害怕/不敢做某事
Tom lost the money and was afraid to tell his mother.
3)be afraid that （从句） 恐怕……
I’m afraid that I’ll be late.
B. Grammar. 定语从句，请看书P。158----159。