When thompson was 5 years of age, he began to complain that his stomach hurt, especially after eating meals and snacks. he also experienced weight loss and chronic diarrhea. his parents noticed that he could eat dairy foods, fruits, and vegetables without developing any intestinal problems, but he would get a "tummy ache" soon after eating sandwiches, crackers, or pancakes. based on this information, thompson's parents should have him tested for?