7. Which of the following statements best differentiates a pure substance from a mixture?

A. A mixture has an even composition throughout while a pure substance doesn't have an even composition.

B. A pure substance is composed of 2 or more components while a mixture has only one component.

C. A solid pure substance melts completely within a short period of time while a mixture melts partially/unevenly.

D. During boiling the temperature of a pure substance varies while that of a mixture remains.​