An Increase in the Temperature of the Reactants Causes an Increase

An increase in the temperature of the reactants causes an increase in the rate of reaction. The best explanation for this behavior is that as the temperature increases,

A) the concentration of reactants increases.
B) the activation energy decreases.
C) the collision frequency increases.
D) the fraction of collisions with total kinetic energy greater than E_a increases.
E) the activation energy increases.