3.只能用whether不能用if的情况

1).在介词后面：

I’m thinking of whether we should go fishing.

We are worried about whether it will rain tomorrow.

2).在动词不定式前：

They asked me whether to go skating.

3).当与or not连用，或提出两种选择时:

I don’t know whether he’s free or not.

Mary asked whether I was doing my homework or not.

Tell me whether you’d like to go shopping or tidy the room.

　4).宾语从句提前时：

　Whether this is true or not, I can’t say.

(二)语序：陈述句语序

　即：主句+连接词+从句(主+谓+其他成分)Do you remember 　_________(他多大岁数)?

(三)时态：

主句用现在时或将来时，从句可用任何时态。 主句用过去时，从句用与过去相关的时态。

2.由从属连词whether, if 引导的宾语从句

if/ whether “是否”，说明对陈述的事物不明确或不清楚。常用在ask, wonder, can(could) you tell me 等后。

1.由从属连词that引导的宾语从句

注：that 在句中无词汇意义，在从句中不能充当成分，在口语当中往往省略

e.g. 　　　　

I hear (that) he will be back in an hour.

He said (that) he missed us very much.

The teacher told us (that) the earth moves around the sun.

2.宾语从句。(注意：时态、语序、人称三个方面)

　①that引导陈述句的宾语从句。在口语中常省略。

　 ②if/whether引导由一般疑问句转变而来的宾语从句。(要用陈述句语序并注意if/whether的区别)

1.掌握can, could, may, might 四个情态动词在表示请求时的用法。

25.Food will be in the form of pills.

24.We will be cared for by robots.

23.Robots could be the first to live on Mars.机器人可能是第一批生活在火星上的(人)。

22.She’s too nervous to relax.

21.Things from Earth are hard to find.= It is hard to find thing from Earth.