下图是形成北半球近地面风的各种力的示意图，据图，下列说法正确的是(　　)

①a是使空气水平运动的水平气压梯度力  ②b使风向偏转的地面摩擦力 

③c是使风向发生变化的水平气压梯度力  ④c是使风向向右偏转的地转偏向力

A．②③

B．①③

C．①④

D．③④

You can't go out since you haven't finished your homework; _____, it is a stormy night. [ ]

A. however

B. suddenly

C. immediately

D. besides