在湖水中划船时，使船前进的动力是[ ]
A、桨对水的推力
B、水直接对船的推力
C、人对船的推力
D、水对桨的推力
答案：D
-- Did you go Dutch after that meal, I mean, with the other five friends?
--- ______.
A．Yes, they did
B．Yes, they paid for the meal
C．No, they didn’t
D．No, because it was my treat that day
地球表面虽然约70%被水所覆盖，但能够直接用于生产和生活的淡水不到（）
A、1%
B、10%
C、20%
