地球最基本的运动形式是（　　）

①水平运动②自转运动③公转运动④垂直运动．

A．①②

B．②③

C．③④

D．①④

Today although           irrigation canal in the picture is still being used , it is no longer

          busy water highway.

A．a ; a

B．a; ;the

C．the; a

D．the ; the