如图3—4所示,一个质量为m的人站在电梯的台阶上,电梯沿图示的方向加速运动时,人随同此电梯一起加速上升.此时,关于人受到的静摩擦力Ff和人对台阶的压力FN有 (
A <img src="https://www.beizhujiaoyu.com/uploads/202208/20130108152915501550.gif" alt="" border="0" /> B <img src="https://www.beizhujiaoyu.com/uploads/202208/20130108152921402140.gif" alt="" border="0" /> C <img src="https://www.beizhujiaoyu.com/uploads/202208/20130108153072167216.gif" alt="" border="0" /> D <img src="https://www.beizhujiaoyu.com/uploads/202208/20130108153046904690.gif" alt="" border="0" />