If an Enzyme-Catalyzed Reaction Has a Velocity of 2 MM/min

If an enzyme-catalyzed reaction has a velocity of 2 mM/min and a V_max of 10 mM/min when the substrate concentration is 0.5 mM, what is the K_M?

A) 0.2 mM
B) 0.5 mM
C) 1 mM
D) 2 mM
E) 5 mM