[填空题]The average cost of natural gas is one third less than that of gasoline at the pump.

[填空题]The average cost of natural gas is one-third less than that of gasoline at the pump.

[填空题]These cost less than usual.

[单项选择]
As the cost of gas and oil for home heating has gone up, many Americans have switched from these fuels to wood for heating their homes. In 1973, approximately 200,000 wood-burning stoves, intended for home use, were sold in the United States; by 1979, this figure had reached one million; and by the end of 1981, there were as many as seven million home owned wood-burning units in operation in the U. S.
In addition to low fuel bills, many people choose these stoves because their initial cost is very low (the prices range from $ 50 kits to $ 5,000 top-of-the-line models), and because new technology has made wood fires more efficient, cleaner, and, therefore, safer than ever before.
One new technological feature of this type is the catalytic(催化) combustor which adds about $ 100 to $ 200 to the cost of the stove, but which causes much more complete combustion (燃烧) of the wood and therefore bums up more of th
A. went up fivefold over a six-year period
B. rose to seven million during the seventies
C. multiplied thirty-five times between 1973 and the beginning of 1981
D. increased by 6,000,000 over an eight-year period

[单项选择]A. They are cheap to buy.
B. They cost less to park.
C. They consume less energy.
D. They are cheaper to repair.

[单项选择]
What is the cost of a one-year membership
A. (A) $600.
B. (B) $650.
C. (C) $700.
D. (D) $1,100.

[单项选择]Carbon dioxide makes up less than one percent of the Earth’s atmosphere, but the gas is very important to life on Earth. Scientists are finding that processes involving carbon dioxide affect our climate in ways that are difficult to understand. Last month, a committee of the National Academy of Sciences in Washington released a report. It confirmed that world temperatures increased about six-tenths of a degree Celsius in the last one hundred years. The report also confirmed evidence that the level of carbon dioxide is increasing.
The best information about climate in the past comes from tests of ice many kilometers deep in Antarctica and Greenland. The tests show changes in temperature during the past four hundred thousand years. These tests show that levels of carbon dioxide today are the highest ever measured.
These findings have led scientists to believe that carbon dioxide is a major cause of climate warming. Carbon dioxide is released into the atmosphere when fuel is
A. ice from Antarctica and Greenland is appropriate to show the change
B. carbon dioxide is released mainly from the fuel
C. global temperatures increase as the level of carbon dioxide increases
D. carbon dioxide is helpful for tree growth