Question

endosymbiosis is the idea that mitochondria and chloroplasts originated when one cell type
became a virus that infects other cells
transferred genetic material to another cell type
engulfed another cell type
began to synthesize atp using aerobic respiration

Explanation:

Endosymbiosis theory posits that mitochondria and chloroplasts originated when one cell type engulfed another. The engulfed cells became symbiotic partners over time.

Answer:

C. engulfed another cell type