单项选择题
A．fly out toward the sun B．look for a new resting place C．come back to their home D．go out and look for food
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