[单项选择]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 re-emphasizes 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 fertil
A. permitted
B. removed
C. proved
D. produced

[单项选择]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 re-emphasizes 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 fertil
A. America relies too much on foreign suppliers
B. the demand of flue vaccines is high this year
C. quality problem is a serious problem in flu vaccine production
D. the supply of flu vaccines is rather weak and America has no back-up measures to make it up