Compare the two phylogenies shown here and choose the best
statement regarding the differences in evolutionary history between
measles and influenza viruses.

A. Measles generates a weak immune response that allows
reinfection of hosts, and therefore does not easily evolve escape
variants.

B. Human influenza A virus evolves escape variants, resulting in
a distinctive cactus-shaped phylogeny.

C. Measles experiences strong selection for escape variants,
resulting in a phylogeny similar to a nonpathogenic species.

D. Human influenza A generates lifelong immunity, so there is no
selection for escape variants.