A 72-year-old man presents to the emergency department with a 6-hour history of severe, diffuse abdominal pain. He has a past medical history diabetes mellitus, hypertension, and colon cancer. Physical exam reveals an abdomen that is extremely tender to light palpation and an irregularly, irregular heart rate. Digital rectal exam is notable for grossly bloody mucous. Laboratory findings are notable for leukocytosis, metabolic acidosis, elevated amylase, and elevated lactate dehydrogenase. Which of the following is the most likely diagnosis?
A. Acute mesenteric ischemia
B. Appendicitis
C. Diverticulitis
D. Pancreatitis