Answer:
A) the origin of eukaryotes
Explanation:
The Endosymbiotic theory talks about how the ancestors of modern eukaryotic cells were once 2+ prokaryotic cells. This theory says that one prokaryotic cell basically lived inside another prokaryotic cell and these cells formed a long term relationship. The prokaryotic cell eventually became a permanent part of the host and eventually evolved into modern day eukaryotic cells.
