Some scientists think that complex eukaryotic cells formed from the union of
two separate prokaryotic cells. The engulfing of one prokaryotic cell by
another is a plausible explanation of why
A,eukaryotic cells lack the defense mechanisms of prokaryotic cells.
B,eukaryotic cells don't share any similarities with prokaryotic cells.
C,organelles in a eukaryotic cell work cooperatively.
D,organelles in a eukaryotic cell would attack other cells.