2021年度四川公共英语考试模拟练习卷（2）新整理版.doc

四川公共英语考试真题卷（2） 本卷共分为1大题50小题，作答时间为180分钟，总分100分，60分及格。 严格遵守考试纪律，维护考试秩序！ 一、单项选择题（共50题，每题2分。每题的备选项中，只有一个最符合题意） 1.Shortages of flu vaccine are nothing new in America, but this year’s is a whopper. Until last week, it appeared that 100 million Americans would have access to flu shots this fall. Then British authorities, concerned about quality-control problems at a production plant in Liverpool, barred all further shipments by the Chiron Corp. Overnight, the U.S. vaccine supply dwindled by nearly half and federal health officials found themselves making an unusual plea. Instead of beseeching us all to get vaccinated, they’re now urging most healthy people between the ages of 2 and 64 not to. This reemphasizes the fragility of our vaccine supply, says Dr. Martin Myers of the National Network for Immunization Information, and the lack of redundancy in our system. Why is such a basic health service so easily knocked out Mainly because private companies have had little incentive to pursue it. To create a single dose of flu vaccine, a manufacturer has to grow live virus in a 2-week-old fertilized chicken egg, then crack the egg, harvest the virus and extract the proteins used to provoke an immune response. Profit margins are narrow, demand is fickle and, because each year’s flu virus is different, any leftover vaccine goes to waste. As a result, the United States now has only two major suppliers ( Chiron and Aventis Pasteur)—and when one of them runs into trouble, there isn’t much the other can do about it. A vaccine maker can’t just call up and order 40 million more fertilized eggs, says Manon Cox, of Connecticut-based Protein Sciences Corp. There’s a whole industry that’s scheduled to produce a certain number of eggs at a certain time. Sleeker technologies are now in the works, and experts are hoping that this year’s fiasco will speed the pace of innovation. The main challenge is to shift production from eggs into cell cultures—a medium already used to make most other vacc