16. Daniel filled a balloon with water to model an organ expanding. He then emptied the water from the balloon to show the organ shrinking. Which organ was he most likely modeling? A. bladder B. liver C. lungs D. pancreas​

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 sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.