I believe the correct match and the answer is C, metabotropic; g protein activation leads to activation of a second messenger. Metabotropic receptors lack opening or closing channels, but instead they are linked to G-protein. When a ligand binds the metabotropic receptor, the receptor activates the G-protein, which in turn activates a second messenger. The second messenger may then, either travel and bind to and open ion channels located on the membrane or the messenger may go and activate other intermediate molecules inside the cell. This varies from one metabotropic receptor to another.
