How is a pure substance different from a mixture? a) pure substances cannot be separated by physical means. b) mixtures cannot be separated by physical means. c) a pure substance is heterogeneous. d) a mixture is made of one substance.

The answer is A.
Pure substance is either an element or a compound, which elements in compund is chemically combined together. They cannot be separated by physical methods such as filtration or evaporation. Compounds can only be separated by chemical methods, which include using electricity (electrolysis) or applying heat.

C: plants and animals