Answer
C. It helped him reason through the results of his experiment.
Step-by-step explanation
When added to ice, salt first dissolves in the film of liquid water that is always present on the surface, thereby lowering its freezing point below the temperature of the ice. Ice in contact with salty water, therefore, melts, creating more liquid water, which dissolves more salt, thereby causing more ice to melt, and so on.
The addition of food coloring could better help him reason through the results of his experiment.
Hence, the correct answer is option C. It helped him reason through the results of his experiment.