All living organisms are composed of

a. only one cell.
b. at least three cells.
c. at least 100 cells.
d. one or more cells.

d:one or more cells

Explanation:

the cell is a basic unit of life and new cells arise from existing cells.

the answer to your question is b

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.