The Forward Rate Constant, K_f, and Reverse Rate Constant, K_r

The forward rate constant, k_f, and reverse rate constant, k_r, for a chemical reaction are not equal.Which statement below must be true?

A) The reaction will be unable to achieve equilibrium.
B) k_f and k_r will become equal as equilibrium is approached owing to concentration changes.
C) k_f and k_r will become equal as equilibrium is approached owing to temperature changes.
D) k_f and k_r will remain unequal, but the rates will become equal owing to concentration changes.
E) k_f and k_r will remain unequal, but the rates will become equal owing to temperature changes.