题干

如图所示,三个质点a、b、c质量分别为m1、m2、M,(M>>m1,M>>m2).a、b在同一平面内绕c沿逆时针方向做匀速圆周运动,它们的周期之比Ta:Tb=1:k.(k>1,为正整数)从图示位置开始,在b运动一周的过程中,则(   )

A:a、b距离最近的次数为k次

B:a、b距离最近的次数为k+1次

C:a、b、c共线的次数为2k次

D:a、b、c共线的次数为2k﹣2次

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D

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    Cleverness is a gift while kindness is a choice.Gifts are easy—they're given after all.Choice can be hard.

    I got the idea to start Amazon 16 years ago.I came across the fact that the Internet usage was growing at 2300 percent per year.I'd never seen or heard of anything that grew that fast,and the idea of building all online bookstore with millions of titles was very exciting to me. I had just turned 30 years old,and I'd been married for a year.I told my wife MacKenzie that I wanted to quit my job and go to do this crazy thing that probably wouldn't work since most start-ups don't and I wasn't sure what to expect.MacKenzie told me I should go for it.As a young boy,I'd been a garage inventor.I'd always wanted to be all inventor,and she wanted me to follow my passion.

    I was working at a financial firm in New York City with a bunch of very smart people and I had a brilliant boss that I much admired.I went to my boss and told him I wanted to start a company selling books on the Internet.He took me on a long walk in Central Park,listened carefully to me,and finally said,“That sounds like a really good idea,but it would be an even better idea for someone who didn't already have a good job.”That 1ogic made some sense to me,and he convinced me to think about it for 48 hours before making a final decision.Seen in that light,it really was a difficult choice,but finally,I decided I had to give it a shot.I didn't think I'd regret trying and failing.And I suspected I would always be haunted by a decision to not try at all.

    After much consideration ,I took the less safe path to follow my passion ,and I'm proud of that choice.For all of us,in the end,we are our choice.