2019年人大国际关系专业考博真题、复习资料.pdf
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1、n dangerous natural chemicalsD) almost all foods have additives(C)23.By saying “they employ chemical warfare” (Line 4, Para. 2), Bruce Ames means “_”.A) plants produce certain chemicals to combat pests and diseasesB) plants absorb useful chemicals to promote their growthC) farmers use man-made chemi
2、cals to dissolve the natural chemicals in plantsD) farmers use chemicals to protect plants against pests and diseases(A)24.The reduction of the possible hazards in food ultimately depends on _.A) the governmentB) the consumerC) the processorD) the grower(B)25.What is the message the author wants to
3、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.(D)Q
4、uestions 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
5、 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 measurements lots of magnetic-field i
6、ntensity 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 long-term decline precedi
7、ng each polarity reversal. When the poles flipa 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 out
8、er core, 3,000 kilometers beneath the earths 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 the
9、y 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 th
10、at 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 earths inner physics. It certainly points the direction for future re
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