What distinguishes reversible inhibitors from irreversible inhibitors?

A) There is an equilibrium between bound and unbound reversible inhibitor. There usually is little back reaction for the binding of an irreversible inhibitor.
B) Reversible inhibitors are not covalently bound to enzymes but irreversible inhibitors are.
C) Reversible inhibitors are easier to purify from solutions of enzymes than irreversible inhibitors.
D) All of the above
E) A and B only