An unconformity represents: a. a gap in the geological record
b. an epeirogenic change
c. a location that was once covered by water
d. an intrusive igneous structure

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.

digestion

it excretes wastes