How can we increase the rate of collisions between the reactants in this reaction? Mg + 2HCl → MgCl2 + H2

A.
Increase the concentration of H2 in the reaction mixture.
B.
Decrease the temperature of the reactants in the reaction mixture.
C.
Increase the concentration of Mg in the reaction mixture.
D.
Decrease the temperature of the entire reaction mixture.
E.
Decrease the concentration of HCl in the reaction mixture.