All Plants Contain Chloroplasts with Both Chlorophyll a and B

All plants contain chloroplasts with both chlorophyll a and b.By comparison,almost all prokaryotic organisms only contain chlorophyll a.One exception is Prochloron,which contains both chlorophyll a and b.According to the endosymbiotic theory,how did photosynthetic plants arise and how did the discovery of Prochloron in the 1970's lend support to this theory?

A) Photosynthetic plants arose from a prokaryote that engulfed another free-living photosynthetic prokaryote that eventually developed into a chloroplast.Given that all plants contain chlorophyll b,it must have been present in the common ancestor of plants.Prior to the discovery of Prochloron,no bacteria were known to contain chlorophyll b.However,the identification of Prochloron,which contains both chlorophyll a and b,suggests that it is the direct descendent of the common ancestor to all plant chloroplasts,and therefore provides conclusive evidence in support of endosymbiosis.
B) Photosynthetic plants arose from a prokaryote that engulfed another free-living photosynthetic prokaryote that eventually developed into a chloroplast.Given that all plants contain chlorophyll a,it must have been present in the common ancestor of plants.Prior to the discovery of Prochloron,no bacteria were known to contain chlorophyll a.However,the identification of Prochloron,which contains both chlorophyll a and b,suggests that it is the direct descendent of the common ancestor to all plant chloroplasts,and therefore provides conclusive evidence in support of endosymbiosis.
C) Photosynthetic plants arose from a prokaryote that engulfed another free-living photosynthetic prokaryote that eventually developed into a chloroplast.Given that all plants contain chlorophyll b,it must have been present in the common ancestor of plants.Prior to the discovery of Prochloron,no bacteria were known to contain chlorophyll b.However,the identification of Prochloron,which contains chlorophyll a,suggests that it is the direct descendent of the common ancestor to all plant chloroplasts,and therefore provides conclusive evidence in support of endosymbiosis.