Section Ⅲ　Grammar--动词不定式&but＋动词不定式

语 境 自 主 领 悟 先观察原句 后自主感悟 1.Scientists have tried many ways to solve this problem and in China，a mass campaign has been started to help solve it.

2.They are often so thick that you cannot see the sun，and the wind is sometimes strong enough to move sand dunes.

3.There was nothing to be done.It was the most frightening and the most dangerous situation I've ever been in.

4.Sandstorms in China appear to have increased in recent years as a result of "desertification".

5.The storms sometimes continue all day and traffic moves very slowly because the thick dust makes it difficult to see.

6.When a sandstorm arrives in the city，weather experts advise people not to go out.

7.The winds are very strong.It's difficult to breathe and the dust makes me ill.

8.To prevent it coming nearer，the government is planting trees.

9.And yet we do nothing but talk about it. 1.1句中，第一个和第二个不定式在句中分别充当状语和宾语；2句和8句中的不定式作状语；5句中，it为形式宾语；7句中，it为形式主语。

2.由6句可知，不定式的否定式为not to do。由3句可知，不定式的被动式为to be done。由4句可知，不定式的完成式为to have done。

3.由9句可知，不定式在介词but后面时，如果but之前有行为动词do的各种形式，则介词后的不定式不带to，否则带to。