Why is it hard to make a good flu vaccine

A) Vaccines take months to make, so people have to guess which strains of flu are going to be active long in advance.
B) The vaccine makers cannot hire the most qualified employees because there is so little profit in making vaccines.
C) Most people do not get flu shots because they like having an excuse to take a day off.
D)The public is uninformed about the way vaccines work, and they do not engage in healthy habits.