The opening ceremony has been put off_____ the bad weather.

A．in case of

B．in spite of

C．instead of

D．because of

如图所示，一运送救灾物资的直升飞机沿水平方向匀速飞行。已知物资的总质量为m，吊运物资的悬索与竖直方向成θ角。设物资所受的空气阻力为F_f，悬索对物资的拉力为F，重力加速度为g，则

A．F_f＝mgsinθ

B．F_f＝mgtanθ

C．F＝mgcosθ

D．F＝