For an Enzyme to Effectively Change Its Activity in Response

For an enzyme to effectively change its activity in response to a change in substrate concentration,it is most favorable for:

A) K_m to be less than cellular substrate concentrations.
B) K_m to be equal to cellular substrate concentrations.
C) K_m to be greater than cellular substrate concentrations.
D) V_max to be at the diffusion limit.
E) The substrate to also be an allosteric effector.