The correct option is D both a and b
Endosymbiosis is a relationship where one organism lives inside the other and both are benefited. The endosymbiotic theory was proposed by Lynn Margulis. It is believed that the ancestral cells engulfed aerobic bacteria and photosynthetic bacteria leading them to evolve into mitochondria and chloroplast respectively, a classic example of “endosymbiosis” called endosymbiotic theory.
With time the engulfed bacteria lost their cell wall and much of their DNA because they were not of any use in the ancestral cell. This is how mitochondria and chloroplasts were formed in the eukaryotic cells.
The earliest organisms are prokaryotes and the prokaryotic cells might have evolved into the eukaryotic cells but it is not the other way.
So, the correct answer is option 'd'.