单项选择题
A．until two o'clock in the morning B．because she wasn't sleepy at all C．because she was busy with her children D．because her husband hadn't finished working
A．to occupy the best resting places B．only when it is dark C．to protect their homes from outsiders D．when there is not enough food
A．double their number every year B．lose a lot of their babies C．move from place to place constantly D．fight and kill a lot of themselves