16、Yellow, orange, red and green tree leaves make autumn a colorful time! Who paints all these colors? It is the leaves themselves.

Inside a leaf, there are millions of little color “bags”. They are green, yellow and orange. The green ones are called chlorophyll (葉綠素).  The yellow ones are called xanthophylls (葉黃素). The orange ones are carotene (胡蘿卜素).

In the summer, the green chlorophyll is very, very busy. It makes food for the tree. It catches sunlight to change water and carbon dioxide (二氧化碳) into sugar. This sugar is the food for the tree. It is also busy that it covers up all of the other colors in the leaf.

 When the weather grows colder in autumn, there is less light and water for trees. The trees will have a rest and get ready for winter. They’ve made enough food in summer! The leaves no longer need water to make food.

Without the water, the green chlorophyll starts to go away. The other colors in the leaf - the yellow xanthophylls and the orange carotene-come out. So the leaves don’t really “turn” a certain color -they just lose their green!

But how about the red, purple and green leaves? The leaves look red or purple because they have some sugar in them. They “steal” some food from the tree! The green leaves are from the evergreen trees (常青樹). Their leaves don’t lose water in winter. So, the green chlorophyll doesn’t go away.

1. The leaves of trees in autumn turn yellow because there is ______.

        A. not enough sunlight. B. no sugar C. no water D. no chlorophyll working

2. The little color “bags” refer to _____

        A. green, yellow and orange     B. chlorophyll, carotene and xanthophylls

        C. carbon dioxide               D. sunlight and water

3. The third paragraph (段) mainly shows us _________.

A. what chlorophyll is         B. how chlorophyll makes water.

C. sugar is food for trees     D. how photosynthesis (光合作用) works

4. Which of the following is NOT TRUE?

A. In summer trees begin to shut down their food-making factories.

B. When autumn and winter come, the days get shorter and shorter.

C. During winter trees rest and live on the food they have stored.

D. In winter little “bags” are still in the leaves.

5. We can infer from the passage that ______.

A. water in the tree leaves makes them green.

B. sugar in the tree leaves makes them yellow.

C. sunlight makes tree leaves green.

D. carbon dioxide makes tree leaves green.