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  3. If we observe carefully, we can find that most of the flowers in nature are red, orange and yellow. If we have seen a black flow

If we observe carefully, we can find that most of the flowers in nature are red, orange and yellow. If we have seen a black flow

admin2009-03-15  71
问题     If we observe carefully, we can find that most of the flowers in nature are red, orange and yellow. If we have seen a black flower, it is a chance in a million. People have made census (普查) to colors of more than four thousand kinds of flowers and discovered that only eight of them are black. Why?
    As we know, sunlight is formed by seven different kinds of colored light. The wave length of each light changes, so the quantity of heat in each light changes, too. Flowers, especially their petals (花瓣) , are very weak and easy to the harm caused by high temperature. Black flowers can take in all the light waves, which cause the flowers to dry up in a high temperature. So the black flowers can hardly continue their lives. But red flowers, orange flowers and yellow ones can protect themselves from sunlight by reflecting (反射) the red light, orange light and yellow light, each of which has a large quantity of heat.
    That is why red, orange and yellow flowers are very common in nature while black flowers are so unusual.
选项 A、they are easy to be eaten by animals
B、there are no black flowers in the world
C、the petals of black flowers are too strong
D、the light waves make the flowers dry up
答案D
解析 从文章第二段的第四、五句可知：由于黑色的花吸收所有的光波，在高温下自然会干死，所以极少能在阳光下幸存，人们也就几乎看不到它们。
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