根据定积分的几何意义，计算${\int }_0^2\sqrt{4-x^2}dx$的结果是（   ）

下列观点符合质量守恒定律的是(  )

关于世界海陆分布的说法，正确的是（     ）

语言严谨的政策文件往往让老百姓觉得“太高冷”。2016年9月，河南省人民政府办公厅印发了《河南省行政机关政策文件解读实施办法》，要求省级行政机关出台的“红头文件”，要将“官话”翻译成大白话，用通俗易懂的语言，把群众关心的事情讲清楚。对“红头文件”进行白话解读（    ）

①尊重了公民参与民主决策和监督的权利

②有利于提高政府文件的科学性和规范性

③是政府践行为人民服务宗旨的具体表现

④有利于群众更好地理解和支持政府工作

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