Answer: option D
Receptors are not classified into 6
Explanation:
Receptors are protein molecules in the cell or cell surface that binds ligands.
Receptors are classified into two, which are;
1.Intracellular or cytoplasmic receptors which are found in the cytoplasm of the cell and the give response to hydrophobic ligand molecules that move across the cell membrane.
2. Cell surface receptors or transmembrane receptors, the are found in the cell surface or cell membrane and they bind to the external ligands molecules.