飞行速度过大使直升机产生振动的主要原因是（）.
A.向前推杆量大
B.旋翼拉力大
C.旋翼空气动力不平衡
参考答案：C
— May I _______ your sport shoes?
— Sure, but you couldn't _______ them to others.
[ ]
A. lend; lend
B. borrow; borrow
C. lend; borrow
D. borrow; lend
上支撑平衡
