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Ann:
Hello, Let me give you a test. 
嗨，让我考考你吧.
Lily:
Ok, just let it out.
好啊，说吧。
Ann:
This morning, my teacher asked us why trees are round not square. Do you know why?
今天早上，我的老师问我们说，树为什么是圆的而不是方的呢？你知道为什么吗？
Lily:
Let me see. I think it is just the order of the nature. They are born round.
让我想想。我想这是自然规律吧，树木天生就是圆的啊！
Ann:
Yeah, I know, but why they are cut out in round shape.
嗯，我知道。但为什么天生就是圆的呢？
Lily:
Err, sorry, I can’t figure it out. Could you give me a hint？
呃，抱歉，我还是想不出来. 能不能给点提示啊？
Ann:
Have you ever found that the corners of the square things always damage easily?
你有没有发现正方形的东西的角都很容易损坏呢?
Lily:
Yes, some of the corners even have been rounded off.
对啊，有的角甚至还被磨圆了呢。
Ann:
The trees are born round so that they can protect themselves.
所以，树木是因为要保护自己才会长成圆的。
Lily:
I got it, the survival of the fittest.
我明白了。适者生存嘛。