A．complicated process, high cost, low profit and high risk
B．shortages of fertilized chicken eggs
C．difficulty in growing live virus
D．fast changing of flu virus

A．the government hopes to solve the problem by way of volunteer restrictions
B．more than 47 million Americans who are qualified to get flu vaccine shots can not get them this year
C．America has to deal with a limited supply of flu vaccines this year
D．normally only a small percentage of American population gets flu vaccine shots each year

A．All Americans are persuaded not to get vaccinated this year.
B．The big problem in innovating flu vaccine producing technique is how to grow virus in a new way.
C．More flu vaccines can not be produced in a short time because private companies refuse to produce more.
D．Flu vaccines are easier than most vaccines to produce through cell cultures.