Parents whose children show a special interest in a sport feel very difficult to make a decision about their children’s careers．Should they allow their children to train to become top sportsmen and sportswomen? For many children it means starting schoolwork very young．And going out with friends and other interests have to take a second place．It’s very difficult to explain to a young child why he or she has to train five hours a day, even at the weekend, when most of his or her friends are playing．
Another problem is of course money, In many countries money for training is available from government for the very best young sportsmen and sportswomen．If this help can not be given, it means that it is the parents who have to find the time and the money to support their child’s development and sports clothes, transport to competitions, special equipment, etc．All can be expensive．
Many parents are worried that it is dangerous to start serious training in a sport at an early age．Some doctors agree that young muscles may be damaged by training before they are properly developed．Professional trainers, however, believe that it is only by training when young that you can reach the top as successful sports person．It is clear that very few people do reach the top, and both parents and children should be prepared for failure even after many years of training．
小题1:Where can we most probably find this passage?
A．An advertisement．
B．A diary．
C．A newspaper．
D．A notice board．小题2:What does the underlined phrase “to take a second place ”in the first paragraph mean?
A．to become less important
B．To put it at another place
C．To happen again
D．They are the most important of all the things小题3:Which of the following statements is true according to the passage?
A．It’s easy to make a decision when your children want to take up sports．
B．Most of the students may become top sports men after a long period of training．
C．Early training may damage young muscles．
D．It’s not very expensive for parents to support their children’s development in sports．
和
，月球半径为
，月球绕地球公转的轨道半径为
，引力常量为
，在月球的环境温度下，水蒸气分子无规则热运动的平均速率为
．则：
，就表明月球表面无水
，就表明月球表面无水
=mg，可求出月球表面的重力加速度．若万有引力小于物体所需的向心力，物体将做离心运动．
，故A正确，B错误．
．水蒸气将做离心运动，可以表明月球表面无水．所以．若