PREMISSION：OTHER TENSES  在其他时态中表示许可

表示许可的can在过去时里可用could:

We could use his pool whenever we wanted to.我们随时都可以用他的游泳池。

而在条件时态里，也可以使用could:

If we were in the USA, I could drive a car at 16.如果我们在美国，16岁我就可以开车。

这时也可以用allow或permit来代替could..例如， 上面过去时态的例子变成下面这样：

We were allowed to use his pool whenever we wanted to.

而上面条件时态的例子可以这么用：

If we were in the USA, I would be permitted to drive a car at 16.

If we were in the USA, they could permit me to drive a car at 16.

其他时态都只能用allow和permit:

Has he ever been allowed to use this phone?他被允许用这部电话吗？

I had never been permitted to go into his room before that day.在那天以前从来不让我进他的屋子。

Will she be allowed to come to the party?她会被允许参加聚会吗？

 

USING ‘CAN’ TO EXPRESS ABILITY  用can表示能力

情态动词can还可以用来表示能力，can只能用在现在时里：

Woman  Can you play the piano and the guitar?你会弹钢琴和吉他吗？

Man     I can play the piano, but I can’t play the guitar.我会弹钢琴，但我不会弹吉他。

过去时态里要用could:

I could read when I was four.我4岁的时候就会阅读了。

I couldn’t swim until I was 15.直到位5岁我才会游泳。

而在条件时态里，要用could这种时态：

If you learne french, you could help me.如果你学了法语，你就可以帮我了。

还可以用be able to来代替上述can和could.例如上面研修例子可以改写成下面这样：

I was able to read when I was four.

I wasn’t able to swim until I was 15.

If you learned French, you would be able to help me.其他时态都必须用be able to :

I have been able to speak Swedish for many years.我会说瑞典语很多年了。

I would love to be able to play a musical instrument.我很希望能演奏某种乐器。

 

USING ‘CAN’ TO EXPRESS POSSIBILITY  用can表示可能性

can还可能用来表示可能，它表示的是一般的可能性性：

In winter, you can ski there.冬天，你可以在那儿滑雪。

You can drive there in less than an hour.开车不到位个你就可以到那儿。

有时届用来表示会发生的可能：The tide here can be dangerous.这儿的湖水很危险。

Mosquitoes can be a problem near the lake.待在湖的附近，蚊子是个问题。

在过去时态里要用could:

We used to live in Canada. In winter, you could ski there. In summer, mosquitoes could be a problem.

 

MULTI-WORD VERBS:WITH ‘UNDER’  under的短语动词

under的基本意思是“在……之下”， 它可以和许多动词一起使用，但惯用句却并不多。

首先，看一下使用字面意思的under词组：

The fox crawled under the fence and escaped.狐狸从篱笆下爬出去逃跑了。

Get under the blanket to keep warm.盖上毯子会暖和点儿。

The sailors tried hard, but eventually the boat went under.船员们努力营救，最终还是沉了。接下来的是under和动词组合后，产生的许多新的意思。