句型转换。

1. Nothing can live without air. (变为同义句)

    Nothing can live if __________ is _________ air.

2. It's about 20 minutes' walk to the farthest restaurant. (就划线部分提问)

    _________ _________ is it to the farthest restaurant?

3. The little girl is too young to stay at home by herself. (变为同义句)

    The little girl ________ old ________ to stay at home _______.

    The little girl is ________ young ________ she can't stay at home by herself.

4. I think math is the most difficult subject of all. (变为同义句)

    I think math is ________ ________ than the ________ subjects.

5. English is more interesting than history. (变为同义句)

    History is _________ interesting ________ English.

    History isn't so _________ as English.

读图完成各题。

图所示的山岭是由于（）

A.背斜形成

B.向斜形成

C.火山喷发形成

D.断层形成