题干

李飞扬给他们指出错误后就去准备运动会铅球比赛项目了,第二天比赛时,他用力向前一推,铅球像离弦的箭飞了出去,斜向上运动到一定高度后又斜着落回地面,取得了比较好的成绩,如果不计空气阻力,关于铅球离开手后的运动过程,下列说法中正确的是(   )

A:铅球出手后因为受到惯性力的作用继续往前飞

B:铅球出手后的上升过程中,李飞扬仍在对铅球做功

C:铅球在下落过程中,铅球机械能总量增大

D:铅球在下落过程中,重力改变了铅球的运动状态

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答案(点此获取答案解析)

D

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             Parents who help their children with homework may actually be bringing down their school grades. Other forms of prenatal involvement, including volunteering at school and observing a child's class, also fail to help, according to the most recent study on the topic.
The findings challenge a key principle of modern parenting(养育子女) where schools except them to act as partners in their children's education. Previous generations concentrated on getting children to 
school on time, fed, dressed and ready to learn.
       Kaith Robinson, the author of the study, said, "I really don't know if the public is ready for this but there are some ways parents can be 
involved in their kids' education that leads to declines in their academic performance. One of the things that was consistently negative was
 parents' help with homework." Robinson suggested that may be because parents themselves struggle to understand the task." They may 
either not remember the material their kids are studying now, or in some cases never learnt it themselves, but they're still offering advice."
       Robinson assessed parental involvement performance and found one of the most damaging things a parent could do was to punish their children for poor marks. In general, about 20% of parental involvement was positive, about 45% negative and the rest statistically
 insignificant.
      Common sense suggests it was a good thing for parents to get involved because "children with good academic success do have involved
 parents ", admitted Robinson. But he argued that this did not prove parental involvement was the root cause of that success." A big 
surprise was that Asian-American parents whose kids are doing so well in school hardly involved. They took a more reasonable approach, conveying to their children how success at school could improve their lives."