Question

About three billion years ago, single-celled organisms called cyanobacteria lived in Earth’s oceans. They thrived on the ocean’s abundance of ___ , which they used during the process of photosynthesis. Much later, this process allowed organisms, such as fish, to survive by extracting dissolved ___ from ocean waters.

a. oxygen
b.carbon dioxide
c. nitrogen

Answer 1

The first blank is carbon dioxide, second one is oxygen

Explanation: That's correct for plato users