题干

观察DNA和RNA在细胞中的分布,所运用的原理是

A:单独利用甲基绿对细胞染色可显示DNA在细胞中分布,从而推知RNA的分布

B:单独利用吡罗红对细胞染色,可显示RNA在细胞中的分布,从而推知DNA的分布

C:利用甲基绿和吡罗红混合染色剂对细胞染色,同时显示DAN和RNA在细胞中的分布

D:在细胞核、细胞质内可分别提取到DNA和RNA,由此说明DNA和RNA的分布

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答案(点此获取答案解析)

C

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阅读理解

    Is lightning dangerous?

    Lightning is beautiful and exciting, but it kills a thousand people in the world

every year. Lightning is electricity. The electricity in lightning is very strong.In 1998, one flash of lightning killed eleven players at a football match.

    What does it feel like?

    Sabrina, aged 12 and her father are lucky to be alive. Last year, they were hit by lightning, but it did not kill them. Sabrina said afterwards, "It felt like a big hammer. My feet and legs hurt for an hour afterwards. My dad said he felt as if his hands were in an electric socket (插座).”

    How far away is it?

    When you see lightning, start counting the seconds: one...two...three....Stop

counting when you hear the thunder. Every three seconds is one kilometer. So if

you count six seconds, the lighting was two kilometers away. That does not mean

it is safe. Lightning can move very fast.

    How to be safe in a storm

    ⒈Stay inside if you can. You will be safe if you do not use the telephone,

electrical equipment or water. Do not stand too close to windows or doors.

    ⒉Lightning often hits metal things, so do not touch metal things outside. But

you are safe in a car if the windows are closed. The electricity goes down through

the car's metal and not through the people!

    ⒊Lighting often hits the tallest thing. Ask yourself "What is the tallest thing there?" If the answer is "A tree", do not stand under that tree. If the answer is "Me", move quickly!