接地速度是指飞机在着陆过程中接地瞬间的速度，影响接地速度的因素有哪些？
参考答案：
飞机重量、空气密度、机翼面积、升力系数。
生物圈是地球上的____________和所在____________的总称。
The plane hasn't arrived yet. Could you tell me ?
[ ]
A. why the plane is late
B. why the plane was late
C. why is the plane late
D. why was the plane late
