Which of the Following Statements Describes a Difference Between a Mixture

Which of the following statements describes a difference between a mixture and a pure substance?

A) A mixture tends to be homogenous, while a pure substance tends to be heterogeneous.
B) A mixture has a specific melting point, while the melting point of a pure substance can vary.
C) The density of a mixture can change with temperature, but the density of a pure substance cannot change.
D) The composition of a mixture can vary from sample to sample, but the composition of a pure substance is always the same.