题目

It will be quite a long time _______ she is back again, so don't be too cross with her. A . that B . since C . before D . until 答案：C1．如图所示，用水平力F将 物体压在一竖直墙壁上，下列说法正确的是（　　）A．物体受到3个力作用B．若物体沿墙壁向下滑动，则F越大，物体所受摩擦力越大C．若物体沿墙壁向下滑动，动摩擦因数为μ，物体所受摩擦力为μmgD．若物体保持静止，则F越大，物体所受摩擦力越大