The _______ - subunit of most heterotrimeric G-proteins binds the guanine nucleotides and acts as a _________.

a. beta, ATPase
b. gamma, GTPase
c. alpha, ATPase
d. gamma ATPase
c. alpha, GTPase

I think the right answer is "E" but not sure please help

E is correct. The alpha subunit has the GTPase activity, the beta, gamma subunits are tightly associated and do not dissociate when activated.