C） To much exercise.
D） Mental strain.
33. According to the passage， alcohol has something to do with bad breath mainly because ______.
A） it keeps offending bacteria from reproducing
B） its smell adds to bad breath
C） it kills some helpful bacteria
D） it affects the normal flow of saliva
34. Mouthwashes are not an effective cure for bad breath mainly because
A）they can't mask the bad odor long enough
B）they can't get to ail the offending bacteria
C） their strong smell mixes with bad breath and makes it worse
D） they can't cover the thick layers of mucus
35. We can infer from this passage that_____.
A） offensive breath can't easily be cured
B） elderly people are less offended by bad breath
C） heavy drinkers are less affected by bad breath
D） offensive breath is less affected by alcohol
Passage 3
“Welcome to the U.S.A.！ Major Credit cards accepted！”
By the millions they are coming-no longer the tired， the poor， the wretched masses longing for a better living .These are the wealthy.“ We don't have a budget ，” says a biologist from Brazil， as she walks with two companions through New York City's South Street. “We just use our credit cards.”
The U.S. has long been one of the world's most popular tourist destinations， but this year has been exceptional. First there was the World Cup， which drew thousands from every comer of the globe； then came the weakening of the U.S. dollar against major currencies. Now the U.S.， still the world's superpower， can also claim to be the world's bargain basement （廉价商品部）。 Nobody undersells America these days on just about everything， from consumer electronics to fashion clothes to tennis rackets. Bottom retail prices-anywhere from 30% to 70% lower than those in Europe and Asia -have attracted some 47 million visitors， who are expected to leave behind $79 billion in 1994. That 's up from $74 billion the year before.
True， not everyone comes just for bargains. There remains an undeniable fascination in the rest of the world with all things American， nourished by Hollywood films and U.S. television series. But shopping the U.S.A. is proving irresistible. Every week thousands arrive with empty suitcases ready to be filled； some even rent an additional hotel room to hold their purchases. The buying binge （无节制） has become as important as watching Old Faithful fountains erupt in Yellowstone Park or sunbathing on a beach in Florida.
The U.S. has come at last to appreciate what other countries learned long ago： the pouring in of foreign tourists may not always be convenient ，but it does put money in the bank. And with a trade deficit at about $130 billion and growing for the past 12 months， the U.S. needs all the deposits it can get. Compared with American tourists abroad， visitors to the U.S. stay longer and spend more money at each stop ；an average of 12.2night and $1624 a traveller versus the Americans， four nights and $298.
36. From what the Brazilian biologist says， we know that tourists like her______.
A） are reluctant to carry cash with them
B） simply don't care how much they spend
C） are not good at planning their expenditure
D）often spend more money than they can afford
37. The reason why 1994 was exceptional is that______
A）it saw an unusually large number of tourists to the U.S.
B）it witnessed a drop in the number of tourists to the U.S.
C） tourism was hardly affected by the weakening of the U.S. dollar that year
D） tourists came to the U.S. for sightseeing rather than for bargains that year
38. By saying “nobody undersells America” （Line 4，Para.3）， the author means that ______.
A） no other country underestimates the competitiveness of American products
B） no body expects the Americans to cut the prices of their commodities
C） nobody restrains the selling of American goods
D）no other country sells at a lower price that America
39. Why does the author assert that all things American are fascinating to foreigners？
A） Because they have gained much publicity through the American media.
B） Because they represent the world's latest fashions.
C） Because they embody the most sophisticated technology.
D） Because they are available at all tourist destinations.
40. From the passage we can conclude that the U.S. has come to realize
A）the weakening if the U.S. dollar can result in trade deficits
B）the lower the retail prices， the greater the profits
C）tourism can make great contributions to its economy
D）visitors to the U.S. are wealthier than U.S. tourists abroad
Passage 4
We sometimes think humans are uniquely vulnerable to anxiety， but stress seems to affect the immune defenses of lower animals too. In one experiment， for example， behavioral immunologist Mark Laudenslager， at the University of Denver， gave mild electric shocks to 24 rats. Half the animals could switch off the current by turning a wheel in their enclosure， while the other half could not. The rats in the two groups were paired so that each time one rat turned the wheel it protected both itself and its helpless partner form the shock. Laudenslager found that the immune response was depressed below normal in the helpless rats but not in those that could turn off the electricity. What he has demonstrated， he believes， is that lack of control over an event， not the experience itself， is what weakens the immune system.
Other researchers agree Jay Weiss， a psychologist at Duke University School of Medicine， has shown that animals who are allowed to control unpleasant stimuli don't develop sleep disturbances or changes in brain chemistry typical of Stressed rats. But if the animals are confronted with situations they have no control over， they later behave passively when faced with experiences they can control. Such findings reinforce psychologists' suspicions that the experience or perception of helplessness is one of the most harmful factors in depression.
One of the most startling examples of how the mind can alter the immune response was discovered by chance. In 1975 psychologist Robert Ader at the University of Rochester School of Medicine conditioned mice to avoid saccharin by simultaneously feeding them the sweetener and injecting them with a drug that while suppressing their immune systems caused stomach upsets. Associating the saccharin with the Stomach pains， the mice quickly learned to avoid the sweetener. In order to extinguish this dislike for the sweetener， Ader re-exposed the animals to saccharin. This time without the drug， and was astonished to find that those mice that had received the highest amounts of sweetener during their earlier conditioning died. He could only speculate that he had so successfully conditioned the rats that saccharin alone now served to weaken their immune systems enough to kill them.
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