Put the following steps of heterotrimeric G protein mediated effector activation in the correct order.
a) GDP binds Gα, Gα separates from Gβγ, GTP binds Gα
b) GTP binds Gα, Gα separates from Gβγ, GDP binds Gα
c) Gα separates from Gβγ, GTP binds Gα, GDP binds Gα
d) GDP binds Gα, GTP binds Gα, Gα separates from Gβγ
