6. Because he was listening to the radio, he didn't hear the knock at the door.

____________________________________________________________________

7. Since / As the weather is so bad, we have to delay our journey.

____________________________________________________________________

8. Now (that) you are grown up, you should not rely on your parents.

____________________________________________________________________

9. A man cannot smile like a child, for a child smiles with his eyes, while a man smiles with his lips alone.

____________________________________________________________________

10. It must have rained last night, for the ground is wet this morning.

____________________________________________________________________

请尝试总结：

1. The use of until ______________________________________________.

2. The use of whether __________________________________________.

3. The use of because __________________________________________.

4. The use of since, now that, as, ________________________________.

5. The use of for ______________________________________________.

Task 2: Learn the following on your own．

1．原因状语从句

引导原因状语从句的连词有：because (因为), since (既然)，now that (既然)，as (由于)， for (因为)

because，since，as和for的区别

四者均可用来表示原因，语气依次由强至弱，区别如下：

(1) 关于 because：语气最强，表示直接原因，可用于回答 why 提出的问题、引导表语从句、用于强调句等，而其余三者均不行：

　　"Why didn't he come?" "Because he was ill." "他为什么没来?" "因为他病了。"

My stomach hurts because I have eaten too many apples. 我肚子痛因为我吃了太多苹果。