Most of the Major Groups of Mammals Arose at the End

Multiple Choice

Most of the major groups of mammals arose at the end of the Cretaceous period.This most likely occurred because

A) hair allowed mammals to exploit colder habitats of a changing climate.
B) differentiation of teeth in mammals allowed them to exploit varied diets.
C) the extinction of non-avian dinosaurs opened niches, allowing mammals to diversify.
D) development of a marsupium allowed mammals to easily migrate with their young.
E) increased oxygen levels allowed mammals to become very large.