Which of the following is true about rocks? a. Rocks are composed of only one mineral. b. Most rocks are a mixture of minerals. c. Coal is not considered a true rock. d. Rocks do not contain any nonmineral matter.

The correct option is B.

Rocks are solid mineral materials that form part of the surface of the earth; they can be exposed on the surface of the earth and they can also be found underneath the earth. Rocks are classified on the basis of their formation and there are different types of rocks. Rocks are considered to be mixtures of different minerals.