8、比较状语从句：than, as

9、条件状语从句：if, unless, so (as) long as, in case, once, a far as, on condition that.

注意if与unless的区别：不能用and连接两个unless从句，即不能有... unless ...,and unless ...。但if ... not and if ... not却不受此限。

You won't lose your weight unless you eat less and unless you exercise more.(×)

但可以说 ... unless you eat less and exercise more.

10、注意状语从句中从句的省略现象

（1）连接词 + 过去分词

Don't speak until spoken to.

Pressure can be increased when needed.

Unless repaired, the washing machine is no use.

（2）连词 +　现在分词

Look out while crossing the street.

（3）连词 + 形容词/其他

常见的有it necessary、if possible、when necessary、if any等。

Step 3 Grammar Review of prepositional phrases

Purpose: To get Ss to know how to use the Grammar

1. Show the following contents on blackboard or PowerPoint.

What's the use of prepositional phrases?

2. Practice To get Ss to have general impression of the grammar through exercises.

3. Conclusion

Purpose: To give brief Instructions of the adverbial clauses

Ask the Ss to make a brief conclusion of the adverbial clauses.