Test each with TesTape. Repeat for 3 trials of each combination. TesTape is used by people who need to test the amount of sugar in their urine because they have diabetes. Thus, TesTape is a very sensitive test for glucose. Lives depend on it working well.
Most people make lactase enzyme when they are young.
As they get older, milk is not as important a part of their diet. Many people no longer make lactase as they get older. They then have trouble digesting dairy products. The lactase enzyme they can no longer produce for themselves can be added to dairy products before they eat them. That is why it was easy to buy lactase for the experiment.