This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
True about G protein-coupled receptors is 
Select and explain. 
A. G proteins bind to hormones on the cell surface, B. All the three subunits alpha, beta and gamma should bind to each other for G protein to act, C. G proteins act as inhibitory and excitatory because of difference in alpha subunit, D. G protein is bound to GTP in resting state
C: G proteins act as inhibitory and excitatory because of difference in alpha subunit
Answer: C: G proteins act as inhibitory and excitatory because of difference in alpha subunit 
Explanation: Heteromeric g protein located inside the cell are activated by g protein coupled receptors that span the cell membrane. Signaling molecules bind to a domain of GPCR out side the cell and an intracellular GPCR domain then in turn activates a paicular G protein Ref:Guyton and Hall textbook of medical physiology 12th edition,page number:540,541,542