According to the endosymbiotic theory, what was the initial relationship between the host cell and the engulfed bacterium?

• A. Mutualistic, where both the host cell and bacterium benefited.
• B. Parasitic, where the bacterium harmed the host cell.
• C. Competitive, where both organisms competed for resources.
• D. Commensal, where only the bacterium benefited.

Answer: (A)