Answer:
He probably suffers from lactose intolerance.
Explanation:
Suffering from lactose intolerance doesn't mean you have to eliminate all kind of lactose from your diet, will depend on the degree of intolerance of the person and the food, since not all lactose have the same concentration
. For example yogurts go through a fermentation process, and have a low lactose concentration, with cheeses, it is recommended to consume those with a greater degree of maturity, since the greater the maturity the less amount of lactose they will contain.
Answer:
in controlled experiment an independent variable is systematically manupulated and dependent variable is measured ; any extraneous variables are controlled
