人体与外界进行气体交换的器官是[ ]
A．呼吸道
B．肺
C．气管
D．支气管
答案：B
Faced with many difficulties, the people in this area wouldn't be willing to _____ to their fates. [ ]
A. get down
B. get through
C. give in
D. give away
轴流状态的滑流理论有哪些基本假设？
