[填空题]The earth’s temperatures will be much lower without the greenhouse gases.

[填空题]The earth’s temperatures will be much lower without the greenhouse gases.

[填空题]Seen from the outer space, the earth is much smaller than the other planets or stars.

[单项选择]How much of the earth’s water can man really use
A. He can use nearly 75% of it.
B. He can use about 97% of it.
C. He can use exactly 3% of it.
D. He can use less than 3% of it.

[单项选择]　　　 Under the Earth’’s topsoil, at various levels, sometimes under a layer of rock, there am 　　　 deposits of clay. Look at cuts where highways have been built to see exposed clay beds; or 　　　 look at a construction site, where pockets of clay may be exposed. Rivers also reveal clay along their banks, and erosion on a hillside may make clay easily accessible. (5)　 What is clay made oF The Earth’’s surface is basically rock, and it is this rock that 　　　 gradually decomposes into clay. Rain, streams, alternating freezing and thawing, roots of 　　　 trees and plants forcing their way into cracks, earthquakes, volcanic action, and glaciers-all 　　　 of these forces slowly break down the Earth’’s exposed rocky crust into smaller and smaller 　　　 pieces that eventually become clay. (10)　 Rocks are composed of elements and compounds of elements. Feldspar, which is the 　　　 most abundant mineral on the Earth’’s surface, is basically made up of the oxides silica and 　　
A. conceal layers of rock
B. can be found in various places
C. are usually small
D. must be removed from construction sites

[单项选择] How Global Warming Works Gases in the Earth’’s atmosphere act like glass in a greenhouse-trapping heat and making life on Earth possible. But there is a delicate balance. Burning coal, oil and natural gas increases atmospheric concentrations of these gases. Over the past century, increases in industry, transportation, and electricity production have increased gas concentrations in the atmosphere faster than natural processes can remove them leading to human-caused warming of the globe. The Sources Of Global Warming The major source of global warming is carbon dioxide pollution from power plants, auto mobiles, and industry. Another source is global deforestation. ●Power plants are responsible for more than a third of U. S. CO2 emissions, yet there are no caps on CO2 emissions from power plants or any other industry. ●Gas guzzling cars and light trucks are also responsible for a third of U.S. CO2 emissions. Current regulations allow fo
A. Y
B. N
C. NG