Question

    Trees are commonly cut down for wood and paper. 1.. The unique chemical process that trees and plants use to turn light energy from the sun into oxygen is known as photosynthesis (光合作用).

2.

The production of oxygen is a result of photosynthesis, but it is not the main purpose of this process. 3.. Plants create their own food through photosynthesis. During this process, a plant’s roots absorb water from the ground, and its leaves take in light energy and carbon dioxide. The plant uses these elements to make fats and proteins that are then used to maintain the plant’s life.

The process of photosynthesis

The first step in photosynthesis is using the sun’s energy. During this process, chlorophyll (叶绿素) absorbs the light energy of the sun. The energy from the sun then acts upon the water absorbed by the roots of the plant. Carbon dioxide sent into the atmosphere by animals and humans is then absorbed by the plant’s leaves and paired with the hydrogen to produce sugar. The sugar is turned into plant food. 4..

Threats to tree photosynthesis

5.. Today, only about 30 percent of Earth’s land is covered in trees. This is contributing to global warming since trees are necessary to consume the carbon dioxide in the atmosphere. Experts believe planting trees is vital in order to ensure the preservation of the delicate balance that enables photosynthesis.

A.The purposes of photosynthesis

B.The advantages of photosynthesis

C.In fact, oxygen is simply a by product

D.It is also responsible for giving plants their green color

E.During this process, extra oxygen is produced and released

F.The trees that change carbon dioxide into oxygen are disappearing rapidly

G.But the greatest value of trees comes from their ability to turn the sun’s energy into chemical energy

Answer

1.G

2.A

3.C

4.E

5.F

【解析】

这是一篇说明文。文章主要说明了树木除了被砍下来作为木材和纸张，其最大的价值在于它的光合作用，并且介绍了光合作用的目的、过程和树木消失对光合作用的威胁。

1.

根据上文Trees are commonly cut down for wood and paper.可知树木通常被砍下来作为木材和纸张。以及后文The unique chemical process that trees and plants use to turn light energy from the sun into oxygen is known as photosynthesis (光合作用).可知树木和植物将太阳光转化为氧气的独特化学过程被称为光合作用。由此可知，本句承接上文说明，树木除了被砍下来作为木材和纸张，其最大的价值在于它的光合作用，可以把太阳的能量转化为化学能。故G选项“但是树木最大的价值在于它们能把太阳的能量转化为化学能”符合语境，故选G。

2.

本空为本段小标题，根据后文The production of oxygen is a result of photosynthesis, but it is not the main purpose of this process.可知氧气的产生是光合作用的结果，但这不是这个过程的主要目的。由此可知，本段主要在说明光合作用的目的。故A选项“光合作用的目的”适合作为小标题，故选A。

3.

根据后文Plants create their own food through photosynthesis. During this process, a plant’s roots absorb water from the ground, and its leaves take in light energy and carbon dioxide. The plant uses these elements to make fats and proteins that are then used to maintain the plant’s life.可知植物通过光合作用产生它们自己的食物。在这个过程中，植物的根从地面吸收水分，叶子吸收光能和二氧化碳。植物利用这些元素制造脂肪和蛋白质，然后用来维持植物的生命。由此可知，植物光合作用的主要目的是为了产生自己的食物，那么氧气实际上只是光合作用的一个副产品。故C选项“事实上，氧只是一个副产品”符合语境，故选C。

4.

本句为本段最后一句，有总结上文的作用，结合上文During this process, chlorophyll (叶绿素) absorbs the light energy of the sun. The energy from the sun then acts upon the water absorbed by the roots of the plant. Carbon dioxide sent into the atmosphere by animals and humans is then absorbed by the plant’s leaves and paired with the hydrogen to produce sugar. The sugar is turned into plant food.可知在这个过程中，叶绿素吸收太阳的光能。来自太阳的能量然后作用在植物根部吸收的水分上。动物和人类排放到大气中的二氧化碳被植物的叶子吸收，并与氢配对产生糖。糖被转化为植物的食物。由此可知，上文描述了光合作用的过程，且提到了二氧化碳被吸收，那么本句就应该提到在光合作用的过程中，才导致了氧气产生和释放。故E选项“在这个过程中，额外的氧气产生和释放”符合语境，故选E。

5.

根据后文Today, only about 30 percent of Earth’s land is covered in trees. This is contributing to global warming since trees are necessary to consume the carbon dioxide in the atmosphere.可知如今，地球上只有大约30%的土地被树木覆盖。这导致了全球变暖，因为树木是消耗大气中的二氧化碳的必需品。由此可知，本句是在说明将二氧化碳转化为氧气的树木正在迅速消失。故F选项“将二氧化碳转化为氧气的树木正在迅速消失”符合语境，故选F。