单项选择题
Influenza virus type A usually produces a mild, self-limited febrile illness in the general population. However, worldwide epidemics have occurred at different times in history due to rapid changes in viral genetic makeup. Which of the following is the most important reason why these sporadic worldwide epidemics occur?
A.Antigenic drift
B.Antigenic shift
C.Hemagglutinin develops the ability to destroy a component of mucin, becoming more infectious
D.Neuraminidase develops the ability to attach to sialic acid receptors, becoming more infectious
E.RBCs agglutinate with certain strains