Guangzhou Evergrande has raised China's hunger for soccer glory ever since the year 2013 ______ a series of its victories over other teams in and abroad China.

A．saw

B．bid

C．had seen

D．had bid

如下图所示装置中，不计滑轮摩擦，当水平向右拉力F＝5 N时，物体恰能匀速向右运动，物体受到的摩擦力为_________N。