The Influenza Virus Contains an RNA Genome

The influenza virus contains an RNA genome.Every year the common flu vaccine is designed to protect against three different strains of the influenza virus.Why do scientists typically have to make a new vaccine every year?

A) The virus can rapidly mutate into new strains.
B) The common influenza virus can come from many species of animals, including cats and dogs.
C) Our bodies develop resistance to the vaccine and it becomes less effective.
D) People change their habits each year and become susceptible to different strains of the virus.
E) The virus develops resistance to the vaccine.