They were abroad during the months when we were carrying out the investigation, or they _____ to our help.

A．would have come

B．could come

C．have come

D．had come

沿水平方向振动的弹簧振子，如图所示，可能的受力情况是（    ）

A．重力，支持力和弹簧的弹力

B重力，支持力，弹簧的弹力和回复力

C. 重力，支持力和回复力

D. 重力，支持力，摩擦力和回复力