题干

下列说法与现代生物进化理论不相符的是

A:马和驴是同一物种,因为它们可以交配并产生骡

B:基因突变、基因重组和染色体变异都是不定向的

C:出现有利变异的个体有更多的机会产生后代从而改变种群的基因频率

D:桦尺蠖的体色变化说明自然选择会影响种群的基因频率

上一题 下一题 0.0难度 选择题 更新时间:2019-11-13 03:44:30

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A

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    Bamboo is one of the world's most useful plants. For thousands of years, bamboo has been used in many different ways-from food to medicine to clothing and, in small ways, as a building material.

    However, bamboo is not often used as a building material in the developed world. A professor at the University of Pittsburgh in Pennsylvania is trying to change that. The professor and his students are testing the strength of bamboo.They are testing how much pressure or weight it can take before breaking.

    Kent Harries is a professor at the University of Pittsburgh. Harries says that testing methods for bamboo need to be the same for all. They need to be standardized. Standardizing test methods for bamboo will help to bring the plant into common use. It will also give engineers and builders around the world a dependable standard.

    Harries says that bamboo is strong in nature. The strength of at least three species of bamboo is similar to steel.Besides its strength, bamboo has other features that make it very useful in building. He says it is resilient(有弹力的), meaning it keeps its shape and strength even under pressure.

    Bamboo also grows quickly. Bamboo that is suitable for construction needs much less resources than wood. The harvest cycle of bamboo is about 3 years. Softwoods such as cedar, pine and spruce have a harvest cycle of about 10 years. And hardwoods that come from flowering plants such as oak and walnut need more than 30 years.

    Bamboo is widely used as food for panda bears. It is also used for flooring and window covers. However, for building, bamboo is not used much outside its native growing area. This is mostly because of its round shape. But there are other reasons too. People think -- or have the mentality--that bamboo is a low quality building material.