Question

Have you ever wondered how and why a fall leaf changes color? We first have to understand what leaves are and what they do.

Plants are the world’s food factories. Plants take water from the ground and take CO2 from the air. Plants use sunlight to turn water and CO2 into glucose(葡萄糖). Glucose is a kind of sugar. Using it as food, plants get energy and grow. Plants using sunlight to turn water and CO2 into sugar is called photosynthesis(光合作用). ChlorophyII helps photosynthesis. It gives plants their green color.

As summer ends and autumn comes, the days get shorter and shorter, and trees ＂know＂ to begin getting ready for winter. During winter, there is not enough light or water for photosynthesis. Trees rest during this time and live on the food they store during the summer. They begin to shut down their food — making factories. As the green chlorophyII disappears from the leaves, we begin to see yellow and orange leaves. These colors have been in the leaves all the time. We just can’t see them in the summer, because they are covered up by the green chlorophyII.

The bright reds and purples we see in leaves are made mostly in autumn. In some trees, glucose is caught in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn turn this glucose into a red color. The brown color of trees is made from waste left in the leaves. It is mixture(混合物) of all these things. It makes the beautiful leaves during autumn.

根据材料内容选择最佳答案。

1.The underline word ＂chlorophyII＂ in the passage means ＂        ＂ in Chinese.

A. 胡萝卜素   B. 叶绿素   C. 氯霉素   D.花青素

2.When they rest in winter, trees live on the food they store during the         .

A. summer    B. autumn   C. winter    D. spring

3.Plants use sunlight to turn         into sugar.

A. water and chlorophyII

B. water and CO2

C. CO2 and glucose  

D. water and glucose

4.Which of the following is NOT true according to the passage?

A. Glucose is a kind of sugar and plants use it as food for energy and growing.

B. Leaves turn red because sunlight and the cool nights of autumn turn glucose into a red color.

C. We can’t see yellow or orange leaves in summer because the two colors are not in leaves.

D. During winter, there is not enough light or water for photosynthesis.

5. What’s the main meaning of this passage?

A. What’s photosynthesis?

B. How and why leaves change colors?

C. Different kinds of leaves.

D. How the seasons change.

Answer

1.B

2.A

3.B

4.C

5.B

【解析】

试题分析：文章主要讲述的是一个落叶是怎样变颜色的。叶绿素帮助光合作用，它给植物提供绿色，在冬天，树以夏天储存的食物为生，植物可以把水和二氧化碳转化成葡萄糖等信息。

1.B词义猜测题。根据短文第一段中的句子“ChlorophyII helps photosynthesis. It gives plants their green color.”可知，叶绿素帮助光合作用，它给植物提供绿色。故答案为B。

2.A细节理解题。根据短文第三段中的句子“ During winter, there is not enough light or water for photosynthesis. Trees rest during this time and live on the food they store during the summer.”可知，在冬天，树以夏天储存的食物为生。答案为A。

3.B 推理判断题。根据短文第三段“Plants use sunlight to turn water and CO2 into glucose(葡萄糖). Glucose is a kind of sugar. ”可以植物可以把水和二氧化碳转化成葡萄糖，这是一种糖，故答案为B。

4.C推理判断题。根据短文第三段中的句子“As the green chlorophyII disappears from the leaves, we begin to see yellow and orange leaves. These colors have been in the leaves all the time. ”可知，这些颜色一直在植物里面。故答案为C。

5.Have you ever wondered how and why a fall leaf changes color?”可知文章主要讲述的一个落叶是怎样变颜色的。故答案为B。

考点：科普类短文阅读。