Which of following statements about G proteins associated with G-protein-coupled receptors is not true?

A. G proteins provide a link between the receptor and effector protein.
B. G proteins can propagate the signal by either the G~ or the G(by) components.
C. G proteins are heterotrimeric.
D. Associated G proteins become active by exchanging GTP and GDP.
E. Activated G protein diffuses away from the receptor.