英语六级1999年1月考试真题及答案（3）
A) They overstate the government's interference with the food industry.
B) They are overoptimistic about the safety of their food.
C) They overestimate the hazards of their food.
D) They overlook the risks of the food they eat.
22.The author considers it impossible to obtain no-risk food because .
A) no food is free from pollution in the environment.
B) pesticides are widely used in agriculture.
C) many vegetables contain dangerous natural chemicals.
D) almost all foods have additives.
23.By saying“they employ chemical warfare”(Line 4, Para. 2), Bruce Ames means “_______”.
A) plants produce certain chemicals to combat pests and diseases.
B) plants absorb useful chemicals to promote their growth.
C) farmers use man-made chemicals to dissolve the natural chemicals in plants.
D) farmers use chemicals to protect plants against pests and diseases.
24.The reduction of the possible hazards in food ultimately depends on .
A) the government. B) the consumer.
C) the processor. D) the grower.
25.What is the message the author wants to convey in the passage?
A) Eating and drinking have become more hazardous than before.
B) Immediate measures must be taken to improve food production and processing.
C) Health food is not a dream in modern society.
D) There is reason for caution but no cause for alarm with regard to food consumption.
Questions 26 to 30 are based on the following passage:
There are some each phenomena you can count on, but the magnetic field, someday is not of them. It fluctuates in strength, drifts from its axis, and every few 100,000 years undergo, dramatic polarity reversal-a period when north pole becomes south pole and south pole becomes north pole. But how is the field generated, and why is it so unstable?
Groundbreaking research by two French geophysicists promises to shed some light on the mystery. Using 80 metres of deep sea sediment(沉淀物)core, they have obtained measurments lots of magnetic-field intensity that span 11 polarity reversals and four million years. The analysis reveals that intensity appears to fluctuate with a clear, well-defined rhythm. Although the strength of the magnetic field varies irregularly during the short term, there seems to be an inevitable longterm decline preceding each polarity reversal. When the poles flip-a process that takes several hundred thousand years-the magnetic field rapidly regains its strength and the cycle is repeated.
The results have caused a stir among geophysicists. The magnetic field is thought to originate from molten (熔化的) iron in the outer core, 3,000 kilometers beneath the earth's surface. By studying mineral grains found in material ranging from rocks to clay articles, previous researchers have already been able to identify reversals dating back 170 million years, including the most recent switch 730, 000 years ago. How and why they occur, however, has been widely debated. Several theories link polarity flips to external disasters such as meteor(陨星)impacts. But Peter Olson, a geophysicist at the Johns Hopkins University in Baltimore, says this is unlikely if the French researchers are right. In fact, Olson says intensity that predictably declines from one reversal to the next contradicts 90 percent of the models currently under study. If the results prove to be valid geophysicists will have a new theory to guide them in their quest to understand the earth's inner physics. It certainly points the direction for future research.
26.Which of the following titles is most appropriate to the passage?
A) Polarity Reversal: A Fantastic Phenomenon of Nature.
B) Measurement of the Earth's Magnetic-Field Intensity.
C) Formation of the Two Poles of the Earth.
D) A New Approach to the Study or Geophysics.
27.The word“flip”(Line 6, Para. 2)most probably means“______”.
A) decline B) intensify C) fluctuate D) reverse
28.What have the two French geophysicists discovered in their research?
A) Some regularity in the changes of the earth's magnetic field.
B) Some causes of the fluctuation of the earth's magnetic field.
C) The origin of the earth's magnetic field.
D) The frequency of polarity reversals.
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