Mixtures are constituted by more than one kind of pure form of matter. We know that dissolved sodium chloride can be separated from water by the physical process of evaporation. However, sodium chloride is itself a pure substance and cannot be separated by physical process into its chemical constituents. Similarly, sugar is a substance which contains only one kind of pure matter and its composition is the same throughout.
Soft drink and soil are not single pure substances. Whatever the source of a pure substance may be, it will always have the same characteristic properties.
Therefore, we can say that a mixture contains more than one pure substance.