题干

曲线a表示使用诱变剂前青霉菌菌株数和产量之间的关系,曲线b、c、d 表示使用诱变剂后青霉菌菌株数和产量之间的关系。下列说法正确的是(    )

①由a变为b、c、d 体现了变异的多方向性;②诱变剂增多了青霉菌的变异方向,加快了变异频率;③d是最符合人们生产要求的变异类型;④青霉菌在诱变剂作用下发生的变异可能有基因突变、基因重组和染色体变异。

A:①②③

B:①③

C:②④

D:②③④

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B

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    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?