You are answering a USMLE-style medical question. Question: A 36-year-old man is brought to the emergency department because of multiple episodes of nonbilious emesis for 3 days. The vomitus consists of undigested food and he has also had dark brown emesis twice today. He has been having early satiety during this period. He has had progressive severe episodic epigastric pain and dyspepsia for the past week. The pain is partially relieved with food or over-the-counter antacids, but worsens at night and several hours after eating. He has also had a weight gain of 2 kg (4.4 lbs) during this period. His father underwent surgery for colon cancer 3 years ago. He has smoked one pack of cigarettes daily for the last 15 years. He drinks two to three beers daily. His temperature is 37.1°C (98.8°F), pulse is 106/min and blood pressure is 108/68 mm Hg. Examination shows dry mucous membranes. The abdomen is mildly tender to palpation in the left upper quadrant; there is a tympanitic mass in the epigastrium. A succussion splash is heard with a stethoscope when the patient is rocked back and forth at the hips. Bowel sounds are reduced. Rectal examination is unremarkable. Test of the stool for occult blood is positive. The remainder of the examination shows no abnormalities. Serum studies show: Na+ 135 mEq/L K+ 3.3 mEq/L Cl- 97 mEq/L Urea nitrogen 46 mg/dL Glucose 77 mg/dL Creatinine 1.4 mg/dL Which of the following is the underlying cause of this patient's vomiting?" Options: A) Inflammation and edema B) Abnormal gastric rotation C) Neoplastic growth D) Walled-off pancreatic fluid collection Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.