比较航天飞机里的物体受到的重力G和支持力N,下面说法中正确的是 ( ) ①航天飞机发射离地时,N>G ②航天飞机返回地面时,N>G ③航天飞机在发射架上等待发射时,N<G ④航天飞机在绕地球运动时,N<G A、①④ B、②③ C、②④ D、①②④ 答案:D —Can you watch TV ________ school nights?—Yes, but I have to be _______ bed ________ ten o’clock.A.in; on; byB.on; on; inC.on, in; byD.in; in; at