题干

在圆轨道上运行的国际空间站里,一宇航员A静止(相对空间舱)“站”于舱内朝向地球一侧的“地面”B上,如图所示,下列说法正确的是

A:宇航员A处于平衡状态

B:宇航员A所受地球引力与他在地面上所受重力相等

C:宇航员A与“地面”B之间无弹力作用

D:若宇航员A将手中一小球无初速(相对于空间舱)释放,该小球将落到“地面”B

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答案(点此获取答案解析)

C

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   Almost every day, we discuss the topic of health, especially for kids. But what is health? “Health” means eating well, getting enough exercise, and having a healthy weight. Let’s read the following rules. They can help you stay healthy.
   1. Eat a variety of food, especially fruit and vegetables. We all know that eating fruit and vegetables can help us stay healthy, but many of us only eat our favorite food. Remember that we can only get the nutrition (营养) we need by eating different kinds of food, especially fruit and vegetables.
   2. Drink water and milk most often. Everyone knows that water is important. Besides that, kids need plenty of calcium (钙) to grow strong bones, and milk is rich in it. Every day, you should drink at least three cups of milk, when you are 9 years old or older. You should also try to have less sugary drinks, like soda and coca. They include a lot of sugar. Sugar only includes calories (热量), not important nutrition.
   3. Listen to your body. When you are eating, notice how your body feels. When your stomach feels comfortably full, stop eating. Eating too much makes you feel uncomfortable. If you do it too often, it can make you unhealthy and fat.
   4. Limit screen time. What's screen time? It's the amount of time you spend watching TV, movies and playing computer games. The more time you spend on these sitting-down activities, the less time you spend playing sports, like basketball, and doing other activities like riding and swimming. Try to spend no more than 2 hours a day on screen time.