15. These photosynthetic organisms can live in extreme environments, sometimes harnessing energy from chemicals, and are among some of the oldest organisms on Earth. Οalgae
O protists
O cyanobacteria
O diatoms

cyanobacteria

Explanation:

the answer of this question the 3rd one, because if you were to think and look up the oldest Bactria it would be that answer.

the backbone of the dna and rna compound is sugar phosphate.

2%? i tried finding the exact sorry if it's not 100% correct ; -;