Bumblebees Pollinate M

Multiple Choice

Bumblebees pollinate M.lewisii,whereas hummingbirds prefer the M.cardinalis.If,by chance,a hummingbird carries M.cardinalis pollen to M.lewisii,the resulting hybrid offspring are viable.M.lewisii and M.cardinalis are different species due to

A) adaptive radiation.
B) gradualism.
C) postzygotic barriers to reproduction.
D) prezygotic barriers to reproduction.
E) independent assortment.