题干

如图所示,在光滑的水平面上放有一物体M,物体上有一光滑的半圆弧轨道,轨道半径为R,最低点为C,两端A、B等高,现让小滑块m从A点静止下滑,在此后的过程中,则(   )

A:M和m组成的系统机械能守恒,动量守恒

B:M和m组成的系统机械能守恒,动量不守恒

C:m从A到C的过程中M向左运动,m从C到B的过程中M向右运动

D:m从A到B的过程中,M运动的位移为 mRM+m

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B

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    When I was seven years old, I got the greatest Christmas gift ever.____Now I realize I actually have the power to be a superhero. I may not able to fly, but I make a difference to someone's life. We all have the power to be a superhero to someone. Here are four ways you can be a real life superhero.

    ____Think about what it is. It could be your support, time, advice, a small gift or a thank-you card. Sometimes, even just the most harmless message can bring someone out of darkness and into the light. It's something that you have to give that can help others.

    Keep yourself healthy.____Look after your body and helping people will be easier. You'll have a clear mind and energy to achieve any task in your way.

    Pick your fight. Every superhero has a battle. It's something that drives them to be the person they are.____It could be anything such as working towards helping reduce the number of homeless people on the street. The fight does not need to be big, but it needs to be powerful.

    Make someone's day. Real life superheroes try to improve the lives of all the people they meet.____You can also try your best to absolutely make someone's day every once in a while. The people who get your help will thank you for it.

A. What's your fight?

B. Stay happy all the time.

C. It was a Batman costume, complete with bell and shoes.

D. Use the things you have to help someone without them.

E. You can't be a superhero if you don't take care of your body.

F. They try their best to turn someone's bad day into a good one.

G. They just want to get up, save the world and forget it ever happened.