Final answer:
The cell membrane is included in all three cells: prokaryotic cells, eukaryotic cells, and cells in general.
Step-by-step explanation:
The type of cell structure that is included in all three cells is the cell membrane. All living cells are surrounded by a cell membrane, which acts as a barrier and regulates the movement of substances in and out of the cell. It is present in both prokaryotic and eukaryotic cells.