What process do scientists think proved earth with oxygen-rich atmosphere?

Which process do scientists think provided Earth with an oxygen rich atmosphere?So how did Earth end up with an atmosphere made up of roughly 21 percent of the stuff? The answer is tiny organisms known as cyanobacteria, or blue-green algae. These microbes conduct photosynthesis: using sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen.

D

Explanation:

D shows a double displacment reaction

the other ones show combustion, synthesis and single displacment