The Rate of a Chemical Reaction Increases with an Increase

The rate of a chemical reaction increases with an increase in concentration of one or more of the reactants.This is best explained by which of the following statements?

A) The increased concentration of the reactants increases the temperature of the molecules.
B) The increased concentration of the reactants increases the activation energy of the reaction.
C) The increased concentration of the reactants increases the speed of the molecules.
D) The increased concentration of the reactants increases the frequency of effective collisions.
E) The increased concentration of the reactants decreases the activation energy.