单项选择题
A. It was destroyed in a fire. B. It was destroyed in a flood. C. It was destroyed in an earthquake.
A. They are flexible and skillful. B. They are too young. C. They are dangerous.
A. they are still working when they are sleeping B. difficult problems will become easier in one’s sleep C. a person’s mind can still be active when he is asleep D. all difficult problems can be worked out during sleep