当直升机产生地面效应时,()增大,则保持悬停所需的功率就减少。
A.阻力
B.发动机转速
C.升力
D.旋翼转速
参考答案:C
We have classes _____ Monday _____ Friday.[ ]
A. at, to
B. from, to
C. from, for
D. on, on
瘦煤的Vdaf>25%.()