Consider the Gas-Phase Equilibrium a B

Consider the gas-phase equilibrium A B. Certain amounts of A and B are mixed in a vessel. As they come to equilibrium

A) the forward reaction rate declines and the reverse reaction rate rises.
B) the reverse reaction rate declines and the forward reaction rate rises.
C) both forward and reverse reaction rates decline.
D) both forward and reverse reaction rates rise.
E) either a or b, but we cannot say which without more information.