What role does mitochondrial DNA play in the context of the endosymbiotic theory?

• A. It implies mitochondria developed DNA independently after the formation of eukaryotic cells.
• B. It supports the idea that mitochondria were once independent organisms.
• C. It indicates mitochondria evolved from the nuclear DNA of eukaryotic cells.
• D. It suggests mitochondria acquired DNA from viral infections.

Answer: (B)