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Carbon Dioxide Passage
The concentration of carbon dioxide in ouratmosphere has been steadily increasing sinceabout 1750. Carbon dioxide lets in sun energy andthen traps it as heat energy, so the more carbon05dioxide in the atmosphere, the higher the averageglobal temperature. Scientists are concerned thateven slight increases in global temperatures willsignificantly affect plant and animal life on Earth.In the past, photosynthesis has been able to keep10the level of carbon dioxide in the air at a lowerlevel. Plants and algae convert water and carbondioxide into oxygen and glucose, using the sun'senergy. Carbon from carbon dioxide becomestrapped or "fixed" as the plant uses glucose to build15cellulose and starches, which make up most of theplant's structure.Human industry is the main cause of increasedcarbon dioxide in the atmosphere. Cutting downforests to make room for expanding cities or farm-20land reduces the amount of carbon dioxide beingremoved. The wood is also often burned, releasingmore carbon dioxide into the air. Burning fossilfuels for energy releases even more carbon dioxidethat had previously been locked up in the coal, oil,25or gas underground.We can reduce the amount of carbon dioxide byreducing how much we release, either by burningfewer fossil fuels or by removing carbon dioxide asthe fuel is being burned. We can burn fewer fossil30fuels by switching to other forms of power thatdon't release carbon dioxide, such as solar or windpower, but these methods are more expensive. Wecan "scrub" the carbon dioxide from the air at thepower plant where the fuel is burned, but that is also35expensive. It is also does not work for the carbondioxide produced by cars, trucks, and airplanes.Reducing our output of carbon dioxide, thougha commendable idea, may not reduce the levelsenough to have a meaningful impact. We might40need to go one step farther and try to remove car-bon dioxide from the air.Many research and development companies arenow developing systems that will act like artificial"trees" and remove carbon dioxide from the atmos-45phere. Several built their approach on a methodused in submarines and space vehicles. They com-bine the carbon dioxide with a strong base calledsodium hydroxide to produce sodium bicarbonate,also known as baking soda. Bubbling air through50a solution of sodium hydroxide works well enoughfor the small amount of air in a space vehicle orsubmarine, but this would be a slow way to processa large amount of air.One researcher found a way to make a plastic55with hydroxide components that would removecarbon dioxide from air as it passes over the surfaceof the plastic. Filters made out of long strands ofthis plastic can then remove carbon dioxide aswind pushes the air through the strands. The filters,60therefore, act much like leaves in a tree.This plastic is inexpensive, but making it intofilters, building towers that contain many "leaves"of the filters, and processing the plastic to removethe carbon dioxide so the plastic can be reused is65currently very expensive. To pay for the cost, gasolinewould end up increasing in price. If manufacturerscould get the cost of this method down to $100 permetric ton of carbon dioxide removed, for example,the price of gas would still have to increase by70about 88 cents to cover the cost. Researchers areoptimistic that they could actually get the cost downto $25 per metric ton. If they achieve this goal, wesomeday may see artificial trees in our cities, assistingthe real trees in cleaning the air.
1. The central idea of this passage is primarily concerned with
2. Which choice provides the best evidence for the answer to the previous question?
3. In paragraph 2, the author helps structure the passage's claim by providing
4. How do the filters described in paragraph 6 act like leaves in a tree?
5. Which of the following examples of evidence would most strengthen the author's line of reasoning?
6. As used in line 11, "convert" most nearly means
7. The passage most strongly suggests that which of the following statements is true?
8. Which choice provides the best evidence for the answer to the previous question?
9. As used in line 38, "commendable" most nearly means
10. Which claim made by the author is supported by the evidence in the graphic?
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