Receptor is a molecule usually found on the surface of a cell, that receives chemical signals from outside the cell. When such external substances bind to a receptor, they direct the cell to do something, such as divide, die, or allow specific substances to enter or exit the cell.Receptors are proteins embedded in either the cell's plasma membrane (cell surface receptors), in the cytoplasm, or in the cell's nucleus (nuclear receptors), to which specific signaling molecules may attach.So, the correct answer is option A.