Answer : The correct answer is -
a. Eubacteria.
Bacteria constitute the simplest forms of life on earth.
Eubacteria is a major branch of bacteria, which includes organisms that are devoid of true nucleus and membrane bound subcellular compartments (cell organelles). Their genetic material is present within the cytoplasm of the cell.
Cyanobacteria (also termed blue green algae) are the photosynthetic bacteria that come under eubacteria.
Thus, option a) Eubacteria is the right answer.