Answer:
The correct answer is - C. retention of their own genome.
Step-by-step explanation:
The endosymbiotic theory is a theory that suggests that eukaryotic cells are developed from prokaryotic cells. According to this theory, organelles like mitochondria are developed in eukaryotic cells as the result of proteo-bacteria cells engulfing aerobic bacteria.
The evidence of this theory can be seen as the mitochondria has their own genome such as circular DNA and ribosomes as the prokaryotes.