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．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
A．laughs at his own joke B．repeats it several times C．is very serious when he tells it D．is concerned about the reaction of his listeners