The Theory of Endosymbiosis proposes the origin of both...

The Theory of Endosymbiosis proposes the origin of both mitochondria and chloroplasts in modern photosynthesizing eukaryotic cells. What was proposed to have occurred in the evolution of these two organelles?

a.

Infoldings of the host cell plasma membrane surrounded the cholorplast to make a double membrane. 

b.

Infoldings of the host cell plasma membrane created the outer membrane of mitochondria.

c.

Aerobic bacteria were engulfed by the host cell.

d.

Cyanobacteria were engulfed (ingested) by the host cell.