Answer:
D.the cells also contain chloroplasts
Step-by-step explanation:
The endosymbiosis hypothesis postulates that organelles such as mitochondrion and chloroplast evolved from free living prokaryotic cells that engulfs one another for mutual benefits.
The theory which was first postulated by Margulis Lynn (1967) explained that aerobic bacteria were ingested by anaerobic bacteria and they co-existed because the relationship is mutually beneficial to both.
The process results in double membrane organelles with their independent genome in eukaryotic cells.
Hence, the presence of either or both of mitochondrion and chloroplast in a cell is an indication that endosymbiosis happened at some point in the history of the discovered cells.
The presence of chloroplast therefore best supports the scientist that thinks endosymbiosis happened at some point in the development of the cells.
The correct option is D.