初中英语语法归纳（十一）

He was doing his homework when I came in.（当）我进来时，他正在做家庭作业

I came in when/while he was doing his homework.当他在做家庭作业时，我走了进来

While/When I was in the town，I saw him twice.（当）我在城里时，见过他两次

Strike while the iron is hot．趁热打铁。．

when还可译作这时while还可译作“而”

He was playing football outside when it began to rain.

他在外面踢足球，这时开始下起雨来。

He is tall while his elder brother is short.

他个子高，而他哥哥个子矮

2. because，since.和as

because引导的从句通常表示说话人认为听话人不知道的原因或理由，从句往往是整个主从复合句的重心。

He was annoyed because he missed the bus. 他感到为难是因为他没有赶上那班车

since和as表示原因时，往往表示人们显然已知的理由或原因；因此，侧重点是主句的内容，原因只作附带说明。在语气上，becausc最强，since次之（在意义上相当于汉语中的“既然”),as最弱

Since his method doesn‘t work，let‘s try yours. 既然他的方法不起作用，我们就试一试你的。

As she was in a bad mood，we left her alone. 由于她心情不好，我们不去打扰她了。

He is absent frorn school because he is ill. 因为他生病，所以他没来上课

Because/As it was wet，we went there by bus. 因为下雨，所以我们乘车去那儿。

Since everybody is here，let‘s begin. 既然大家都到了，我们就开始吧。

3.if和unless

引导条件状语从句的连词，主要是if和unless,由if条件状语从句可以是真实的条件句，也可以非真实条件句．真实条件句所表示的条件指的是事实，即可以是实现的事，非真实条件句指的是与事实相反或不大可能实现的事．

If it rains, the match will be cancelled（取消）． 如果天下雨，比赛将被取消

If I were you, l should consult（请……看病）a doctor. 我要是你，我就去看医生

If I had tried hard last term，I would have succeeded. 如果上学期我努力的话，我现在就已经成功了

unless在意义上相当于if... not

You will fail unless you work harder. 除非你努力，否则你不会成功。