State one advantage of using a stain to study frog skin cells with a microscope

Most cells are transparent or colorless and therefore staining  helps make them visible and thus they can be studied under the microscope in better detail. Staining usually works by using a dye that stains some of the cell components a bright color, together with a counterstain that stains the rest of the cell a different color.

 There are many different ways of staining. The method used can either be non-specific where most of the cells are stained in much the  same way, or specific where particular components within the cell or tissue are stained selectively. 

i am positive it is c. condensing but i may be wrong