用一弹簧测力计把物体从一粗糙的斜面匀速拉上去,以下说法正确的是( )
A:木块只受到拉力、滑动摩擦力两个力
B:弹簧测力计的读数大于滑动摩擦力
C:木块的速度越大,滑动摩擦力越大
D:弹簧测力计的读数等于滑动摩擦力
I haven't seen my grandma for a long time. I can't help her very much.
图中的河流R,一般情况下,( )