What Were Ron Fouchier and Colleagues Trying to Find Out

What were Ron Fouchier and colleagues trying to find out with their serial passage experiment in ferrets?

A) how the global spread of bird flu could be prevented
B) the number of people that could die in a future bird flu outbreak
C) how bird flu evolved the capacity to establish itself in the human airway
D) the mutations that would give bird flu the capacity to spread from person to person