A:①③
B:②④
C:①②
D:③④
8n是整数,正整数n的最小值是( )
一个重为2N的长方体木块,在水平桌面上做匀速直线运动时,受到的水平拉力为0.6N,若水平拉力增大为0.8N时,此时木块受到的摩擦力与合力的大小分别为( )
—Excuse me. Where is school library? —This way, please.