我国是世界上手机用户最多的国家,手机是通过 ____传递信息的.这种“波”在空气中的传播速度约为 ____m/s.
读图,完成下列各题。
— Now I must go _______ I shall be late for the train. — Have a good trip. Goodbye.
The red-crowned crane is one of _______ in the world.