<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 30-year-old caucasian female comes to the physician because of chronic diarrhea and abdominal bloating that started 6 months ago. She also reports increasing fatigue and intermittent tingling in her hands and feet. She lost 5 kg 11 lb of weight over the past 6 months without changing her diet or trying to lose weight. She and her husband have been trying to conceive for over a year without any success. Menses have been irregular at 2845 day intervals and last for 12 days. She has generalized anxiety disorder for which she takes sertraline. Her height is 151 cm and weight is 50 kg; BMI is 22 kgm2. Examination shows generalized pallor. Cardiopulmonary examination is normal. Test of the stool for occult blood is negative. Laboratory studies show:Hemoglobin 9.5 gdLLeukocyte count 3900mm3Platelet count 130,000mm3SerumGlucose 100 mgdLCreatinine 0.6 mgdLThyroid-stimulating hormone 3.3 μUmLVitamin B12 80 pgmL N 200IgA anti-tissue transglutaminase antibody negativeSerum IgA decreasedWhich of the following is the most appropriate next step in diagnosis?? A: Plasma zinc concentration, B: Fecal fat test, C: IgG deamidated gliadin peptide test, D: IgA endomysial antibody, E: Skin prick test,  <response>: This is a question about diagnosing the cause of chronic diarrhea and other symptoms in a 30-year-old woman. The key findings are chronic diarrhea, abdominal bloating, fatigue, tingling in hands and feet, weight loss, irregular menses, pallor, low hemoglobin, leukopenia, thrombocytopenia, low vitamin B12, and decreased serum IgA. The differential diagnosis includes celiac disease, inflammatory bowel disease, intestinal malabsorption, and autoimmune disorders. Celiac disease is a likely possibility given her symptoms of diarrhea, weight loss, irregular menses, and decreased serum IgA. The next best diagnostic test would be IgG deamidated gliadin peptide DGP to detect antibodies against gluten, which is elevated in celiac disease. Choice A tests for zinc deficiency which does not fit her presentation. Choice B tests for fat malabsorption which is less likely. Choice D tests IgA endomysial antibodies which will be falsely negative given her IgA deficiency. Choice E does not test for a gastrointestinal condition.C: IgG deamidated gliadin peptide test 