The Cell Membrane Is Often Referred to as Asymmetrical or "Mosaic".This

The cell membrane is often referred to as asymmetrical or "mosaic".This means that

A) both layers of the phospholipid bilayer are not identical in terms of protein type or number and phospholipid type.
B) only certain substances can pass through the phospholipid bilayer freely,while others require the help of membrane proteins.
C) the phospholipids of the membrane can flip-flop such that phospholipids from the inner layer are exchanged with those from the outer layer.