A:C3H6、C4H6O2
B:C2H6、C2H6O
C:C2H2、C6H6
D:C3H6O、C3H8O
校园里有15棵松树,37棵杉树.松树的棵数是杉树的____。杉树的棵数是松树的____。
下列关于在斜面上自由下滑物体的受力分析示意图中,正确的是( )
Most students spend too much time ________ computer games.