To cause a human pandemic, the h5n1 avian flu virus would have to
a. spread to primates such as chimpanzees.
b. develop into a virus with a different host range.
c. become capable of human-to-human transmission.
d. become much more pathogenic.

c. become capable of human-to-human transmission.

Explanation:

The H5N1 flu virus is a virus that is capable of causing infectious respiratory disease in birds and hence, it is an avian influenza virus and the infection caused by it famously known as bird flu. When it comes to humans, the humans may acquire the infection from consuming or being in close contact with infected birds however, the incidences of the human pandemic are rare. The reason for fewer chances of a human pandemic is because for such a pandemic to occur person to person spread is needed which does not happen in case of bird flu.