In Influenza Virus,antigenic Shift

In influenza virus,antigenic shift

A) results from reassortment of genomes when two different strains of flu viruses infect the same cell.
B) results from the accumulation of mutations in HA and NA in a single strain of flu virus.
C) can result in major epidemics or pandemics.
D) results from reassortment of genomes when two different strains of flu viruses infect the same cell and can result in major epidemics or pandemics.