They're all common in the fact that they have to eat others that have energy, because they in themselves cannot produce their own energy. All animals are multicellular.
The correct answer is option C, that is, mammals were able to diversify to make use of the variety of habitats that were previously occupied by dinosaurs.
Adaptive radiation refers to the comparatively fast evolution of various species from a single common ancestor. Adaptive radiation usually takes place when a species enters a novel area and distinct traits influence its existence. An illustration of adaptive radiation is the progression of mammals after the annihilation of dinosaurs.