In this case, the best method for Linh to determine what liquid was used to dissolve the other substances is distillation.
Distillation allows for the separation of a solvent from dissolved substances based on differences in boiling points. By heating the solution, the liquid (the solvent) can evaporate and then be condensed back into a liquid in a separate container, leaving behind the other substances. This method is effective for identifying the solvent used in a solution, making it the most suitable choice for Linh's analysis.
Evaporation could also isolate the solvent, but it doesn’t allow for the collection of the solvent, and filtration and decantation are not typically used for separating solutions for identifying the solvent.