Question: Which concept supports the endosymbiotic origin of complex, eukaryotic double-membrane structures?

  Options: 
 A. Mitochondria and chloroplasts arise from preexisting mitochondria and chloroplasts.
 B. Mitochondria and chloroplasts arise from preexisting endomembrane systems.
 C. Mitochondria and chloroplasts are synthesized in the nucleus.
 D. Mitochondria and chloroplasts are synthesized in ribosomes.
Answer: A