The correct response is:
Phagocytosis, a type of endocytosis, was used by a prokaryote to engulf a second prokaryote.
This process is related to the endosymbiotic theory, which proposes that certain organelles within eukaryotic cells, such as mitochondria and chloroplasts, originated from prokaryotic cells that were engulfed by an ancestral eukaryotic cell through mechanisms similar to phagocytosis. This engulfing process allowed for a symbiotic relationship, leading to the evolution of complex eukaryotic cells.