A:46,44+XX
B:46,44+XY
C:24,22+XY
D:23,22+X或Y
There were some children ____ (play) football on the playground.
(2015•锦州)如图所示,木块A与平板小车一起在水平桌面上向左匀速直线运动,当小车受外力作用突然减速时,木块随机在小车的平板上滑行,请画出木块滑行过程中的受力示意图.