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肿瘤细胞不表达MHC-I类分子产生免疫逃逸，杀伤这类肿瘤细胞的主要是（）
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16Passage OneQuestions 46 to 50 are based on the following passage.As a person who writes about food and drink for a living. I couldn't tell you the first thing about Bill Perry or whether the beers he sells are that great. But I can tell you that I like this guy. That's because he plans to ban tipping in favor of paying his servers an actual living wage.I hate tipping.I hate it because it's an obligation disguised as an option. I hate it for the post-dinner math it requires of me. But mostly, I hate tipping because I believe I would be in a better place if pay decisions regarding employees were simply left up to their employers, as is the custom in virtually every other industry.Most of you probably think that you hate tipping, too. Research suggests otherwise. You actually love tipping! You like to feel that you have a voice in how much money your server makes. No matter how the math works out, you persistently view restaurants with voluntary tipping systems as being a better value, which makes it extremely difficult for restaurants and bars to do away with the tipping system.One argument that you tend to hear a lot from the pro-tipping crowd seems logical enough: the service is better when waiters depend on tips, presumably because they see a benefit to successfully veiling their contempt for you. Well, if this were true, we would all be slipping a few 100-dollar bills to our doctors on the way out their doors, too. But as it turns out, waiters see only a tiny bump in tips when they do an exceptional job compared to a passable one. Waiters, keen observers of humanity that they are, are catching on to this; in one poll, a full 30% said they didn't believe the job they did had any impact on the tips they received.So come on, folks: get on board with ditching the outdated tip system. Pay a little more upfront for your beer or burger. Support Bill Perry's pub, and any other bar or restaurant that doesn't ask you to do drunken math.1. What can we learn about Bill Perry from the passage?A) He runs a pub that serves excellent beer.B) He intends to get rid of the tipping practice.C) He gives his staff a considerable sum for tips.D) He lives comfortably without getting any tips.2. What is the main reason why the author hates tipping?A) It sets a bad example for other industries.B) It adds to the burden of ordinary customers.C) It forces the customer to compensate the waiter.D) It poses a great challenge for customers to do math.3. Why do many people love tipping according to the author?A) They help improve the quality of the restaurants they dine in.B) They believe waiters deserve such rewards for good service.C) They want to preserve a wonderful tradition of the industry.D) They can have some say in how much their servers earn.4. What have some waiters come to realize according to a survey?A) Service quality has little effect on tip size.B) It is in human mature to try to save on tips.C) Tips make it more difficult to please customers.D) Tips benefit the boss rather that the employees.5. What does the author argue for in the passage?A) Restaurants should calculate the tips for customers.B) Customers should pay more tips to help improve service.C) Waiters deserve better than just relying on tips for a living.D) Waiters should be paid by employers instead of customers.
In the past, falling oil prices have given a boost to the world economy, but recent forecasts for global growth have been toned down, even as oil prices sink lower and lower. Does that mean the link between lower oil prices and growth has weakened?Some experts say there are still good reasons to believe cheap oil should heat up the world economy. Consumers have more money in their pockets when they're paying less at the pump. They spend that money on other things, which stimulates the economy.The biggest gains go to countries that import most of their oil like China, Japan, and India, But doesn't the extra money in the pockets of those countries' consumers mean an equal loss in oil producing countries, cancelling out the gains? Not necessarily, says economic researcher Sara Johnson. “Many oil producers built up huge reserve funds when prices were high, so when prices fall they will draw on their reserves to support government spending and subsidies(补贴)for their consumers.”But not all oil producers have big reserves, In Venezuela, collapsing oil prices have sent its economy into free-fall.Economist Carl Weinberg believes the negative effects of plunging oil prices are overwhelming the positive effects of cheaper oil. The implication is a sharp decline in global trade, which has plunged partly because oil-producing nations can't afford to import as much as they used to.Sara Johnson acknowledges that the global economic benefit from a fall in oil prices today is likely lower than it was in the past. One reason is that more countries are big oil producers now, so the nations suffering from the price drop account for a larger share of the global economy.Consumers, in the U.S. at least, are acting cautiously with the savings they're getting at the gas pump, as the memory of the recent great recession is still fresh in their mind. And a number of oil-producing countries are trimming their gasoline subsidies and raising taxes, so the net savings for global consumers is not as big as the oil price plunge might suggest.1. What does the author mainly discuss in the passage?A) The reasons behind the plunge of oil prices.B) Possible ways to stimulate the global economy.C) The impact of cheap oil on global economic growth.D) The effect of falling oil prices on consumer spending.2. Why do some experts believe cheap oil will stimulate the global economy?A) Manufacturers can produce consumer goods at a much lower cost.B) Lower oil prices have always given a big boost to the global economy.C) Oil prices may rise or fall but economic laws are not subject to change.D) Consumers will spend their saving from cheap oil on other commodities.3. What happens in many oil-exporting countries when oil prices go down?A) They suspend import of necessities from overseas.B) They reduce production drastically to boost oil prices.C) They use their money reserves to back up consumption.D) They try to stop their economy from going into free-fall.4. How does Carl Weinberg view the current oil price plunge?A) It is one that has seen no parallel in economic history.B) Its negative effects more than cancel out its positive effects.C) It still has a chance to give rise to a boom in the global economy.D) Its effects on the global economy go against existing economic laws.5. Why haven't falling oil prices boosted the global economy as they did before?A) People are not spending all the money they save on gas.B) The global economy is likely to undergo another recession.C) Oil importers account for a larger portion of the global economy.D) People the world over are afraid of a further plunge in oil prices.
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