In G-Protein Coupled Receptor (GPCR) signaling, the following events must occur in this order: Select one: a. GPCR binds ligand, a GEF protein is recruited to activate the alpha-subunit, beta and gamma-subunits are inhibited, alpha-subunit activates effector proteins b. GPCR binds ligand and all subunits dissociate away from plasma membrane to activate other effector proteins c. GPCR binds ligand, GTP is exchanged for GDP in alpha-subunit, alpha-subunit separates, and all subunits activate effector proteins d. the GPCR binds ligand, GDP is exchanged for GTP in alpha-subunit, alpha-subunit separates, and all subunits activate effector proteins