Today's Diversity of Mammals Originated with an Adaptive Radiation That

Multiple Choice

Today's diversity of mammals originated with an adaptive radiation that occurred 65 million years ago.This adaptive radiation occurred because

A) ecological niches were opened up and predators were removed.
B) the evolution of a novel trait that gave the animals an advantage.
C) the ancestral species colonized a new continent.
D) increased competition led to rapid natural selection.