单句语法填空

1.Only if you work hard                  you pass the test.

2.I haven't visited my teacher                I graduated.

3.They got up early in the morning                 (catch) the early bus.

4.Who wrote a book explaining how animals and plants developed                the environment changed?

5.Try                 (knock) on the back door if there is no answer on the front door.

6.The sunlight is white and blinding,                 (throw) hard­edged shadows on the ground.

7.I got up late this morning.This is                 I was late for school.

8.I became confident enough                 (challenge) the good tennis players.