Explanation:

Option c is correct: The cell membrane, also called the plasma membrane, is found in all cells and separates the interior of the cell from the outside environment. The cell membrane consists of a lipid bilayer that is semi-permeable. The cell membrane regulates the transport of materials entering and exiting the cell. The plasma membrane is flexible and is made up of organic molecules called lipids and proteins. However, we can observe the structure of the plasma membrane only through an electron microscope. The flexibility of the cell membrane also enables the cell to engulf food and other material from its external environment. Such processes are known as endocytosis. Amoeba acquires its food through such processes.