Which is not a topic of biology? a. the distribution of sand on an ocean floor
b. the chemicals at work in the stomach
c. the speed at which a hummingbird flies

explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.

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.