Question: For the α subunit of a trimeric G protein (A.) a G-protein-coupled receptor (GPCR) acts as a guan…

For the α subunit of a trimeric G protein

(A.) a G-protein-coupled receptor (GPCR) acts as a guanine
nucleotide exchange factor (GEF), whereas a regulator of G protein
signaling (RGS) can act as a GTPase-activating protein (GAP).

(B.)a GPCR acts as a GAP, whereas an RGS can act as a GEF.

(C.)Both a GPCR and an RGS can act as a GEF

(D.)both a GPCR and an RGS can
act as a GAP.