题干

老鼠毛色有黑色和黄色之分,这是一对相对性状.下面有三组交配组合,请判断四个亲本中是纯合子的是(    )

交配组合

子代表现型及数目

①

甲(黄色)×乙(黑色)

8(黑):9(黄)

②

乙(黑色)×丙(黑色)

12(黑):4(黄)

③

甲(黄色)×丁(黑色)

全为黑色

A:甲和乙

B:乙和丙

C:丙和丁

D:甲和丁

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答案(点此获取答案解析)

D

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阅读理解。

阅读短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项。

    Camping wild is a wonderful way to experience the natural world and, at its best, it makes little environmental influence. But with increasing numbers of people wanting to escape into the wilderness, it is becoming more and more important to camp unobtrusively(不引人注意地)and leave no mark.

    Wild camping is not permitted in many places, particularly in crowded lowland Britain. Wherever you are, find out about organizations responsible for managing wild spaces, and contact them to find out their policy on camping and shelter building. For example, it is fine to camp wild in remote parts of Scotland, but in England you must ask the landowner's permission, except in natural parks.

    Camping is about having relaxation, sleeping outdoors, experiencing bad weather, and making do without modern conveniences. A busy, fully-equipped campsite(野营地)seems to go against this, so seek out smaller, more remote places with easy access to open spaces and perhaps beaches. Better still, find a campsite with no road access: walking in makes a real adventure.

    Finding the right spot to camp is the first step to guaranteeing a good night's sleep. Choose a campsite with privacy and minimum(最小化的) influence on others and the environment. Try to use an area where people have obviously camped before rather than creating a new spot. When camping in woodland, avoid standing dead trees, which may fall on a windy night. Avoid animal runs and caves, and possible homes of biting insects. Make sure you have most protection on the windward side. If you make a fire, do so downwind of your shelter. Always consider what influence you might have on the natural world. Avoid damaging plants. A good campsite is found, not made—changing it should be unnecessary.