A:
B:
C:
D:
如图甲所示,完全相同的木块A和B叠放在水平桌面上,在12N的水平拉力F1作用下,A、B一起作匀速直线运动,此时木块B所受的摩擦力为____ N;若将A、B紧靠着放在水平桌面上,用水平力F2推A使它们一起匀速运动(如图乙所示),则推力F2=____ N.
操场上原来有多少人跳绳?
____ ____ ____ = ____ (____)
—All the people of Jiangyin need to work together to make our city more beautiful.
—That's it. _______.
我国领土中的最南部分在 ( )