The endosymbiont theory states that chloroplasts originated a) from cyanobacteria entering and remaining in the cytoplasm of another cell. b) through evolutionary change in a mitochondrion. c) by fusion of several prokaryotes. d) by spontaneous generation in the cytoplasm of an ancestral cell. e) by fusion of mitochondria and peroxisomes.

The endosymbiotic theory states that chloroplast originated from A Cyanobacteria entering and remaining in the cytoplasm of another cell.

Explanation:

Endosymbiotic theory in an important theory of evolution which states that Eukaryotic cells are originated from prokaryotic organism.

        The theory deals with the fact that chloroplast and mitocondria were free living prokaryotic organism at Past. The similarities between prokaryotic cell and these Eukaryotic organelles(Mitocondria,Chloroplast) and the evolution of mitocondria and chloroplast from the prokaryotic cells is best exlained by the theory of endosymbiosis.

Mitocondria evolved from the Endocytosis of aerobic bacteria,whereas Choroplast are originated from photosynthetic bacteria such as cyanobacteria.