Why is the tunica intima, the innermost layer of arteries and veins, made of epithelial cells?

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.

a) carbon, hydrogen

b) carbon, hydrogen, oxygen, nitrogen

c) carbon, hydrogen, oxygen, nitrogen, phosphorus

d) sugar

e) amino acid

f) nucleotide