The correct answer is: c) both prokaryotes and eukaryotes.
Explanation: Both prokaryotic and eukaryotic cells have a cell membrane, which is crucial for maintaining the integrity of the cell and regulating the movement of substances in and out of the cell. The cell membrane is a fundamental structure present in all living cells, regardless of their complexity. Prokaryotes, such as bacteria, have a simple cell structure without a nucleus, while eukaryotes, which include plants, animals, and fungi, have a more complex structure with a defined nucleus. However, the presence of a cell membrane is a common feature that unites both cell types.