According to the theory of endosymbiosis, the origin of chloroplasts probably involved:_______
a) the formation of colonies of cyanobacteria.
b) the formation of cell walls around the photosynthetic pigments.
c) engulfing of small photosynthetic prokaryotes by a larger cell.
d) the accumulation of free oxygen in ocean waters.
e) infolding of the cell membrane around circular pieces of DNA in the cytoplasm.