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Filtration is a method that separating insoluble material from the liquid, allowing the liquid to pass through a porous material.
most of all not Evaporation, the method of evaporating liquid into a gas.
Decantation The process of allowing a mixture stand in order for the solid and liquid layers to separate. 
Chromatography used in the different degrees to which substances are absorbed on the surface of an inert substance,  such as filter paper.

the problem associated with the separation of liquid " clear water " into  the muddy water at the bottom of the container. so, my answer is letter C, decantation.