根据下面每段话的陈述内容，选出各段恰当的主题，并将其字母序号填入题前括号内。

（D）

    ____ The world use 1 million plastic（塑料） bags every minute. They can now be found in all parts of the world.

    ____ When I was young, I thought space was wonderful. I spent all day imagining that I h ad my own spaceship. That was my earliest dream.

    ____ In Brazil, people wear white clothes on New Year's Eve, because it brings good luck. At midnight people go to the sea and throw flowers into the sea and make wishes.

    ____ Over hundreds of years the Earth gets hotter and then it gets colder again. The world is getting warmer now.

    ____ Sometimes, good things happen because of mistakes. Once I got on the wrong train. That was a big mistake. But I saw a friend on that train.

A. Climate (气候) change.   

B. The plastic bag problem.

C. New Year in Brazil.      

D. Making mistakes is not always bad.   

E. My childhood dream

②∵ ${\left(x-\frac{1}{3}\right)}^2$ ≥0，∴ ${\left(x-\frac{1}{3}\right)}^2$ + $\frac{1}{2}$ ＞0.

模仿上述方法解答：

求证：

“没有逃避的地方，只有冲锋打仗。没有平安幸福，只有互相杀戮。”——《蒙古史书》