用适当的冠词a,an,the或"／"填空
1. This is____useful book. I've read it for hour.
2. _____elephant is much heavier than ____horse.
3. _____doctor told him to take______medicine three times____day.
4. Let's go out for _____walk.
5. There is____woman over there.____woman is Meimei's mother.
6. ____sun rises in_______east.
7. ______Changjiang River is______longest river in_______China.
8. Are you going to do it____second time?
