Correct Option: B

Cyanobacteria, also known as blue algae, are singlecelled and belong to the family of Prokaryotes. That means, they do not have a cell nucleus. The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early reducing atmosphere into an oxidizing one, which dramatically changed the composition of life forms on Earth by stimulating biodiversity and leading to the nearextinction of oxygen-intolerant organisms.