Why Were Mammals Able to Become the Dominant Species at the Beginning

Multiple Choice

Why were mammals able to become the dominant species at the beginning of the Cenozoic?

A) The mammals were finally able to grow legs and come out of the ocean to populate the land.
B) The dinosaurs died off and the small rodent-like mammals of the Mesozoic evolved to fill the niche.
C) The amphibians who first walked on land died out because it was too cold for them,after which mammals with fur took over.
D) Mammals evolved from primates after the dinosaurs went extinct and became the top predator.