The right answer is C) cell membrane. (it could not be the cell wall because this latter is labeled J in the picture).
A cell membrane distinguishes a fundamental cellular structure formed from a double layer of phospholipids associated with other lipids, proteins and carbohydrates.
The membrane of the cell, also known as the plasma or cytoplasmic membrane, is a biological membrane (biomembrane) that separates the interior of all cells from the external environment.