30. Which of the following series best reflects what we know about how the flu virus moves between species?
(A) An avian flu virus undergoes several mutations and rearrangements such that it is able to betransmitted to other birds and then to humans.
(B) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat thepig products can be infected.
(C) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differentlyand then pass it back to humans.
(D) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the newvirus mutates and is passed to a new species such as a bird, the virus mutates and can be transmitted tohumans.