What is the main idea of the Endosymbiotic Theory?

Endosymbiotic theory proposes that these organelles were once prokaryotic cells, living inside larger host cells. The prokaryotes may initially have been parasites or even an intended meal for the larger cell, somehow escaping digestion. The endosymbiotic theory states that eukaryotic cells might have evolved from prokaryotic cells through a close realtionship. hope it helps

Explanation:

the answer is c) an oak tree

answer; i believe the correct answer is (a)0