题干

下列关于“核酸是遗传物质的证据”的相关实验的叙述,正确的是(   )

A:噬菌体侵染细菌实验中,用32P标记的噬幽体侵染细菌后的子代噬菌体多数具有放射性

B:肺炎双球菌活体细菌转化实验中,R型肺炎双球菌转化为S型菌是基因突变的结果

C:肺炎双球菌离体细菌转化实验中,S型菌的DNA使R型菌转化为S型菌,说明DNA是遗传物质,蛋白质不是遗传物质

D:烟草花叶病毒感染和重建实验中,用TMV A的RNA和TMV B的蛋白质重建的病毒感染烟草叶片细胞后,可检测到A型病毒,说明RNA是TMV A的遗传物质

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答案(点此获取答案解析)

D

同类题5

阅读下列短文,根据短文内容选择最佳答案。

                                                                           C

    Flying is a fast way to travel. But it is a big headache for some people. They can't help worrying about things like, “Is turbulence (颠簸) a bad thing?” or, “Is it dangerous if we don't change our mobile phones to flight mode (飞行模式)?” British newspaper Daily Mail spoke to some experts to answer these questions. They also tell us other interesting things about flying.

    Is turbulence dangerous?

    It's scary and uncomfortable. But it is not something you really need to worry about.

    Turbulence is caused when two groups of air hit one another at different speeds. Wind, thunderstorms (暴风雨) and being close to mountains can be reasons for this.

    You may feel like turbulence is dangerous, but it won't crash (坠毁) your plane. “Even in extremely rough air (扰动气流), the wings (机翼) are not going to break off,” explained Patrick Smith, an airline pilot, who is also an air travel blogger and author of Ask The Pilot. com.

    Why are plane windows round?

    Round windows are for passenger safety.

    As the airplane flies higher and higher, the outside atmospheric pressure (气压) gets lower and lower. During the flight, the pressure inside the plane becomes greater than the pressure outside.

    When this happens, square windows can break. That's because having different pressures inside and outside puts pressure on the corners of square windows. But rounded corners can spread the pressure through the window.

    What happens when a phone isn't on flight mode?

    Some passengers believe mobile phones and tablets need to be turned off because they could bring the plane down. However, this is not true.

    If you don't change your phone to flight mode, pilots and air traffic controllers may hear unpleasant sounds in their headphones. It also influences radio communications. So it's still best to put it on flight mode.