题干

汽车尾气中的CO在四氧化三钴(Co3O4)纳米棒的催化作用下,低温即与O2反应生成CO2。下列关于该反应的说法中,正确的是( )

A:该反应是分解反应

B:反应前后Co3O4化学性质改变

C:反应前后碳元素的化合价不变

D:可降低汽车尾气对大气的污染

上一题 下一题 0.0难度 选择题 更新时间:2014-12-26 01:46:08

答案(点此获取答案解析)

D

同类题2

阅读理解

    You never played the video dance game? Now such games are used to help lose weight!

    Like many other teenage boys, Jones loves sports. But at 5 feet, 175 pounds, he found his weight in trouble. His doctor wanted him to lose 50 pounds so that he may be a good football game player by the end of the summer.

    Jones chose the popular Dance Revolution video game at home to increase his activity. He had lost about 10 pounds by changing his diet. Now, after two weeks' playing the game, he has lost another 10!

    A health study is being done by an insurance company. The company hopes that the game will lead to better health and lower costs. “Obesity claims last year cost us $ 77 million. We have to cut those costs,” said a member of the insurance group. The company provides a game console (游戏主机), a dance mat and software for the six-month, $ 60,000 study.

    The study is more than a commercial thing of an insurance company. It is widely supported by physical education and health professionals.

    In West Virginia, 43% of the nearly 6,000 children examined for heart disease risk were considered over-weighted; more than 25% were too fat. “We are in a crisis of childhood obesity not only in West Virginia but in America,” said a researcher.

    Researchers are now looking at the potential for improving effects by using the game. A teacher in West Virginia has been using the video games in her classes since last fall. She reported that the game does improve heart health as well as eye-hand coordination (协调能力), and her students take the video game as a great alternative to jumping rope or ball games.

    The US Education Department is putting the game in 20 schools to control childhood obesity. Well, are you going to try such to dance away your extra weight?

同类题5

根据短文理解,选择正确答案。

    What will man be like in the future—in 5,000 or even 50,000 years from now? We can only make a guess, of course, but we can be sure that he will be different from what he is today, for man is slowly changing all the time.

    Let us take an obvious example. Man, even five hundred years ago, was shorter than he is today. Now, on average, men are about three inches taller, so we may assume (假定) that man will continue to grow taller. Again, as time goes on, we shall have to use our brains more and more. This is likely to bring about a physical change to the head, in particular, the forehead will grow larger.

    Nowadays our eyes are in constant use. In fact, we use them so much that very often they become weaker and we have to wear glasses. But over a very long period of time it is likely that man's eyes will grow stronger.

    On the other hand, we are likely to make less use of our arms and legs, which, as a result, are likely to grow weaker. At the same time, however, our fingers will grow more sensitive because they are used a great deal in modern life.

    But what about hair? This will probably disappear from the body altogether in course of time because it does not serve a useful purpose any longer.

    Perhaps all these give the impression that in the future man will not be a very attractive creature to look at! This may well be true. All the same, in spite of all these changes, future man will still have a lot in common with us.