A Researcher Studies the Evolutionary Relationships Between Influenza Viruses by Comparing

A researcher studies the evolutionary relationships between influenza viruses by comparing the genomic sequences of the viruses found in pigs, ducks, and humans in a given year.When evaluating the viruses that had infected these hosts the previous year, she identifies a cross-species transfer from humans to pigs.This information supports the hypothesis that cross-species transfer leads to more severe disease if during the previous year

A) humans suffered a severe influenza pandemic.
B) pigs suffered a severe influenza pandemic.
C) ducks suffered a severe influenza pandemic.
D) both humans and ducks suffered severe influenza pandemics.
E) both pigs and ducks suffered severe influenza pandemics.