Most periods of rapid evolutionary change are preceded by what type of event? A. Natural Disaster B. Climactic event C. Competition D. polymorphism

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

the answer is d.) homologous; have mammary glands