Scientists Develop New Vaccines for Flu Every Year Because of the

Scientists develop new vaccines for flu every year because of the

A) high rate of infection by the influenza virus in humans.
B) long incubation time of the influenza virus in the human body.
C) high rate of mutation of the influenza virus.
D) long generation time of the influenza virus.
E) low rate of transmission of influenza virus from person to person.