Answer:
Directional
Explanation:
In population genetics, for natural selection to occur there must be a variation that will favor the survival of an individual.
Directional selection is a form of natural selection that occurs in the extreme end when an environment condition such as food favors one phenotype over the other.
This will make the allele Frequencies to shift towards the direction of the superior phenotype.
Viral infection by consuming animal diet is very common these days. These generally cause global pandemic. Most of the pandemic virus are influenza virus, which causes flu like symptoms in humans as well animals including birds, and poultry animals.
The H1N1 virus, which a Influenza A virus causes many type of infections, which includes Swine flu, Cat flu etc. The cat flu is a flu, which is known to be caused by eating cats. The viruses are well known to evolve and mutate easily and cause the changes in the subtype. The mutations in subtypes of viruses makes it difficult to make a vaccine for these types of flu.
Hence, the first blank can be filled with Subtypes, second blank can be filled with Influenza A and the third blank can be filled with Cat Flu.
C. carbon monoxide is the answer