[单项选择]A concentration of carbon dioxide in the atmosphere would______.

[单项选择]The concentration of carbon dioxide is caused by_______.
A. the heat accumulated in the atmosphere
B. the burning of coal
C. the wide use of renewable energy
D. the destruction of the tropical rain forest

[单项选择]It can be concluded that a concentration of carbon dioxide in the atmosphere would ______.

[单项选择]Plants can absorb the carbon dioxide through their ______ during the sunlight hours and produce oxygen which human beings need to survive.
A. slots
B. hoses
C. pores
D. sponges

[单项选择]Why researchers put trees in extra carbon dioxide in the first study
A. To learn whether trees can still absorb carbon dioxide under extreme conditions.
B. To get more oxygen from these trees.
C. To evaluate the maximum carbon dioxide that trees can absorb.
D. To see the growth rate of these trees.

[单项选择]

In the atmosphere, carbon dioxide acts rather like a one-way mirror -- the glass in the roof of a greenhouse which allows the sun’s rays to enter but prevents the heat from escaping. According to a weather expert’s prediction, the atmosphere will be 3~C warmer in the year 2050 than it is today, if man continues to burn fuels at the present rate. If this warming up took place, the ice caps in the poles would begin to melt, thus raising sea level several metres and severely flooding coastal cities. Also, the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere, possibly resulting in an alteration of the earth’s chief food-growing zones. In the past, concern about a man-made warming of the earth has concentrated on the Arctic because the Antarctic is much colder and has a much thicker ice sheet. But the weather experts are now paying more attention to West Antarctic, which may be affected by only a few degrees of
A. prevent the sun's rays from reaching the earth's surface
B. mean a warming up in the Arctic
C. account for great changes in the climate in the northern hemisphere
D. raise the temperature of the earth's surface

[单项选择]According to the passage, carbon dioxide serves which of the following functions for fire ants
A. (It protects the queen
B. ( It attracts other ant species
C. ( It informs workers of possible danger
D. ( It encourages the ants to gather together

[单项选择]The process by which carbon dioxide and oxygen are transferred does not depend on_______.
A. the presence of nitrogen in the blood
B. the muscles of the thoracic cavity
C. the flow of blood
D. the moisture in the air sac linings

[单项选择]If the percentage of carbon dioxide in the air continues to increase at current rates ______.
A. average daily temperatures worldwide could increase considerably
B. some sea level islands could be threatened by flooding
C. all coastal regions throughout the world could be at serious risk
D. all of the above

[单项选择]Cutting carbon dioxide emission by 60% will ______.
A. be reached when low-income countries agree to reach an agreement
B. cause a collapse of the world economy
C. reduce in a large amount the content of CO₂in the atmosphere
D. help realize a stabled world economy

[单项选择]All the following are parts of the sun's atmosphere except ____________.
A. the corona
B. the chromosphere
C. the photosphere
D. the core

[单项选择]The concentration of populations in cities has given ______ to many problems of housing, education, and medical services.
A. rise
B. reason
C. result
D. response

[单项选择]There is large concentration of ownership today ______.
A. although competition among them has increased
B. so the quality standards from them have declined
C. and this means that the qualifications of reporters is declining
D. but the standards among newsrooms has improved over the years