5. There were several variables in this experiment, including the amount of water in each cup, the number of drops of food coloring, the color of the food coloring, and when the coloring was added to the water. Pick one of these variables and explain why you think it was important to keep it the same in both cups.​

There are no choices given but we can still have an answer for this problem. We can assume that each choice is a cup that is made of different metal. Metals are very good conductor of heat but different metals are better. Thermal conductivity is the information we need to know here. The higher the thermal conductivity the faster the cup will increase it's temperature.