题目

在《验证机械能守恒定律》的实验中，打点计时器所接交流电频率为50Hz，当地重力加速度g=9．80m/s2。实验选用重锤质量为m（kg），从所打纸带中选择一条合适的纸带，此纸带第1、2点间的距离应接近             。纸带上连续的点A、B、C、D至第1点O的距离如上图所示（O点为开始下落点），则重锤从O运动到C，重力势能减少_______           _____J，重锤经过C时其动能增加              J。    Many studies show that children around the world are becoming less active and less physically fit. The result is an increase in I he condition of being overweight and having other diseases.  It is a major concern to public health officials. And it may be that fitness levels affect (影响) more than physical health. For students? it may also affect test scores.  In Redondo Beach,California,more than 700 children recently are walking to school with parents and,in some cases,even their dogs. The students do this once a week. The children may not know it but walking helps reduce fat. It also means to increase their activity,or fitness levels.  "Its a good way to make the kids exercise in the morning."  For the kids,it's just fun.  "I like walking to school with my friends."  "Elissa is one of my friends. And we talk about a lot of things at school. We talk about how hard our homework is and all of the fun activities we're doing."  A study from the US Centers for Disease Control and Prevention shows that most American children are physically unfit. But children in other countries also face this problem.  The World Health Organization advises that children between 5 and 17 get at least 60 minutes of physical activity every day.  Studies on children and exercise show that fitness is good for more than just physical health.  A US Institute of Medicine study shows that physical activity helps students with their studies. Harold Kohl led the study. He is a professor at the University of Texas. He researches how diseases spread among populations.(   ) 1. Which is NOT true about over 700 children in Redondo Beach,California?   A. Walking to school means to increase their fitness.   B. They walk to school with their parents or dogs.   C. Walking to school is a good way to make the children exercise.   D. They walk to school with their parents every day.(   ) 2. The underlined word "reduce" means "         ” in Chinese.   A. 放松   B.熄灭   C. 减少   D. 增加(   ) 3. A study from the US Centers for Disease Control and Prevention shows that         .   A. children need an hour of exercise every day   B. most American children are physically unfit   C. physical activity helps students with their studies   D. children are becoming less active(   ) 4. Which is TRUE according to the passage?   A. Fitness levels may affect test scores.   B. Fitness is just good for physical health.   C. Only American kids are physically unfit.   D. Harold Kohl led the US Centers for Disease Control and Prevention.(   ) 5. The passage mainly tells us       .   A. the children's scores   B. the children's homework   C. the children's health   D. the children's diseases