3．that　先行词被 the only 修饰，定语从句中缺主语，故用 that 引导。

　　4．that　先行词被形容词的最高级修饰，定语从句中缺主语，故用 that 引导。

　　5．that　先行词既有人又有物时，定语从句用 that 引导。

　　6．when　先行词为时间名词，定语从句中缺状语，故用 when 引导。

　　7．as　先行词被 such 修饰，定语从句中缺宾语，故用 as 引导。

　　8．as　先行词被 so 修饰，定语从句中缺主语，故用 as 引导。

　　9．why　先行词为 the reason，定语从句中缺状语，故用 why 引导。

　　10．in which/that　先行词为 the way，定语从句中缺状语，故用 in which/that 引导。

　　Ⅱ.语法填空

　　Mary: It's eight o'clock now. Why did you get back so late today?

　　Alan: The buses were __1__ crowded during the rush hour that it took me a long time to get on a bus. And then my bus got __2__ (stick) in the traffic jam.

　　Mary: I'm sorry to hear that.

　　Alan: What __3__ buying a car now?

　　Mary: Do you really think __4__ necessary?

　　Alan: Yes, quite necessary. You see, every day I have to spend a long time __5__ (travel) on the road so that I can get to work on time. If I have a car, it will be much __6__ (easy) for me.

Mary: You have a point there. But I don't think we have enough