问题 选择题

下列过程中,不是化学变化的是:(   ) 

A.铁锅生锈

B.煤气燃烧

C.石蜡熔化

D.大米酿酒

答案

答案:C

本题考查的是化学变化和物理变化的判别,化学变化是指有新物质生成的变化,物理变化是指没有新物质生成的变化,化学变化和物理变化的本质区别是否有新物质生成。

A、在铁锅生锈过程中,有新物质铁锈生成,是化学变化,所以错误;

B、在煤气燃烧过程中,有新物质二氧化碳生成,是化学变化,所以错误;

C、在石蜡熔化过程中,只是石蜡的状态发生了变化,没有新物质生成,是物理变化,所以正确;

D、在大米酿酒过程中,有新物质酒精生成,是化学变化,所以错误。故选C

阅读理解

阅读理解。

     Over ten years ago, the world's populating stood at 6 billon. By the end of October, it has reached

7 billion.

    With five babies being born every second , 78 million people are added to earth each year. The

population was fewer than I billion in 1800 , 3 billion in 1960and 6 billion as recently as 1999.

    According to the United Nations, the next landmark statistic will be 8 billion iii 2025. Much of the

increase can be accounted by the world ' s poorest nations, which are expected to double their numbers

over the next decade.

    "With. the population still growing by about 80 million each year, it's hard not to be alarmed. "Said

Robert Kunzig, author of an article entitled 7 Billion in National Geographic Magazine.

    "Right now on Earth , water tables are falling, soil is being eroded (侵蚀),g laciers are melting, and

fish stocks are vanishing. Close to a billion people go hunger each year. "

     Researchers say the world's population will level off at about 9 billion in the middle of the century,

"How we're going to feed 9 billion people by 2050 is a daunting question." Mr. Kunzig said.

1. What's the population of the world over ten years ago according to the passage?

A. 7 billion.

B. 6 billion.

C. 8 billion.

D. 9 billion.

2. Which of the following statement is TRUE?

A. The poorest nations have the largest population.

B. It is not a problem to feed 9 billion people.

C. Some people don't have enough food to eat in the world.

D. Every family has two children at least in Western Europe.

3. The underlined phrase "level off" may be the meaning of ______.     

A. 减少           

B. 稳定          

C. 增加  

D. 迅增

4. What will probably the population of the earth be in the middle of the century?

A. 6 billion.

B. 7 billion.

C. 8 billion.

D. 9 billion.

5. What is the article mainly about?  

A. The population of the world.      

B. The population of poor nations     

C. The population of Western Europe. 

D. The environment of the earth.

选择题