句型转换。按要求完成下列句子，每空一词。

1. There used to be a lot of old city walls in Beijing, _____ _____?(改为反意疑问句)

2. I think the old city walls are useless. (对画线部分提问)

    _____ _____ you think of the old city walls?

3. Let's go out for a walk, _____ _____? (改为反意疑问句)

4. The Great Wall is about 6000 kilometers long. (对画线部分提问)

    _____ _____ is the Great Wall?

5. I spend about10 minutes in walking to my school every day. (改为同义句)

    It _____ me 10 minutes _____ walk to my school every day.

花键联接一般用于定心精度要求不高和载荷较大的动联接和静联接。