如图所示,放手后纸片不能保持静止,这样的操作是为了探究物体在平衡状态下所受的两个力( )
A:大小是否相等
B:方向是否相反
C:是否作用在同一物体上
D:是否作用在同一直线上
我们战胜困难与挫折的必由之路是( )
—Are all the students from in your class?
—No, there are only three in our class. The others are from other countries.