Most Heterogeneous Reactions Are Slower Than Similar Homogeneous Reactions

Most heterogeneous reactions are slower than similar homogeneous reactions. Which of the following best explains why?

A) The temperature of the two phases is different.
B) Heterogeneous mixtures are not allowed to react, and therefore are heterogeneous.
C) Heterogeneous mixtures require the use of a catalyst.
D) The ability of reactants to come in contact with each other in heterogeneous mixtures is limited by the different phases.
E) The activation energy of heterogeneous reactions is always much higher.