A patient has icterus for 2 weeks, no abdominal pain. US enlargement of gallbladder. The most feasible cause of disease is:
A. Gallblader obstruction with stone
B. Chronic pancreatitis caused by bile-duct obstruction
C. Tumor of pancreas head
D. Acute cholecystitis
E. Alcoholic hepatitis
Answer: C. Tumor of pancreas head