A. Lipid bilayer: the phospholipid bilayer is the membrane of a cell. The bilayer contains lipids, membrane proteins, cholesterol, receptors for various molecules, pumps to transport ions and solutes against the concentration gradient, and many other items necessary for a cell to function and work together with other cells.
b. Osmotic pressure: Osmosis is the flow of water across a semipermeable barrier from an area of low solute concentration to high solute concentration. Osmotic pressure is the lowest possible pressure to prevent this water movement.
c. Endoplasmic Reticulum: the Rough ER synthesizes proteins for use outside the cell. The Smooth ER produces lipids and some steroidal hormones.
A. Lipid Bilayer is therefore the correct answer. Osmotic pressure does not involve the various components of the cell membrane, and the ER's produce proteins and hormones. Therefore A is right.
Hope this helps! :) Let me know if you need a clarification.
