The correct option is C Sand and water
Filtration is a method for separating insoluble solids from the liquid.
For example: When a mixture of sand and water is filtered, the sand stays in the filter paper (residue) and the water passes through the filter paper (filtrate).
Solutions such as salt water and sugar water cannot be separated using a filter paper. This is because solutions do not have insoluble components.
Also, milk and water is a colloid. But the components are not large enough to get filtered out.