题目内容

________ trees there are，________ the environment we have.


  1. A.
    The more；the best
  2. B.
    The less；the least
  3. C.
    The worse；the worst
  4. D.
    The more；the better
D
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　　Yellow, orange, red and green- tree leaves make autumn a colourful time! Who paints all these colours? It is the leaves themselves. Inside a leaf, there are millions of little colour“bags”, they are green, yellow and orange. The green ones are called chlorophyll（叶绿素）.The yellow ones are called xanthophylls（叶黄素）. The orange ones are called carotene（胡萝卜素）.

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

　　When the weather grows colder in autumn, there is less light and water for trees. The trees will have a rest to 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 colours in the leaf-the yellow xanthophylls and orange carotene come out. So the leaves don't really“turn”a certain colour. 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 （常绿树）. The evergreen trees stay green all year long. Their leaves don't lose water in winter.

　　Read the passage then choose True(T) or false (F).

(1) The tree leaves have the following colour“bags”, such as green, yellow and orange except red.

(　　)

(2) In summer, the green chlorophyll works hard for the tree leaves.

(　　)

(3) In autumn, the tree leaves turn yellow or orange because the green chlorophyll stops working and goes away.

(　　)

(4) Tree leaves no longer make food in summer.

(　　)

(5) We can infer（推断）from the article that trees can clean the air.

(　　)

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