以靠空气为依托的航空器向上飞行的最高限度为空气空间最高界，—般离地（水）面约（）公里。
参考答案：30—40
It's nearly eight o'clock. I must hang up and get down to work. My boss _____ be here at any moment.[ ]
A. should
B. must
C. could
D. would
具有清肺止咳功效的药物是
A．海金沙
B．石韦
C．冬葵子
D．灯心草
E．赤小豆
