题干

关于平衡力,下列说法中正确的是(   )

A:物体在平衡力的作用下,一定保持静止状态

B:作用在物体上的两个力三要素完全相同,这两个力一定是平衡力

C:物体受到重力和拉力的作用,这两个力方向相反,它们一定是平衡力

D:运动物体在平衡力的作用下,一定保持运动状态不变

上一题 下一题 0.0难度 选择题 更新时间:2014-06-05 03:16:32

答案(点此获取答案解析)

D

同类题3

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项。

    Many facts suggest that children are overweight (超重的) and the situation is getting worse, according to the doctors. I feel there are a number of reasons for this.

    Some people blame the fact that we are surrounded by shops selling unhealthy, fatty foods, such as fried chicken and ice cream, at low prices. This has turned out a whole generation of grown-ups who seldom cook a meal for themselves. If there were fewer of these restaurants, then probably children would buy less take-away food.

    There is another argument that blames parents for allowing their children to become overweight. I agree with this, because good eating habits begin early in life, long before children start to visit fast food shops. If children are given fried chicken and chocolate rather than healthy food, or are always allowed to choose what they eat, they will go for sweet and salty foods every time, and this will carry on throughout their lives.

    There is a third reason for this situation. Children these days take very little exercise. They do not walk to school. When they get home, they sit in front of the television or their computers and play computer games. Not only is this an unhealthy pastime (消遣), it also gives them time to eat more unhealthy food. What they need is to go outside and play active games or sports.

    The above are the main reasons for this problem, and therefore we have to encourage young people to be more active, as well as steering them away from fast food shops and bad eating habits.