题目

Boys need friends, suffer when they don’t believe they have any, and worry over the ups and downs of relationships. Many adults believe that somehow boys need friends less than girls do, in truth, though, no boy is an island: boys value their friends throughout childhood and adolescence and are happier and healthier when they have solid relationships with peers. Despite the common belief that girls are better at relationships, most boys consider their friends a very important part of their lives, and boys may actually be better at keeping friendships than girls are. A recent study of下列描述的物体中，受到平衡力作用的物体是A.正在加速向上飞的运载火箭B.正在减速的汽车C.正在沿弧形轨道快跑的四驱车D.静止在桌面上的粉笔盒