This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
Which of the following are causes for cholecystitis wxcept? 
Select and explain. 
A. Estrogen, B. OCP, C. Diabetes mellitus, D. Obesity
C: Diabetes mellitus
Answer: C: Diabetes mellitus 
Explanation: acalculous cholecystitis is not an uncommon entity, but can be commonly missed.* It is common in patients who have undergone major surgeries, trauma, burns, or any other stress or in cases of cholecystoses. * Common in ICU patients. ACUTE CHOLECYSTITIS * Commonly it occurs in a patient with pre-existing chronic cholecystitis but often also can occur as a first presentation. * Usual cause is impacted gallstone in the Hamann's pouch, obstructing cystic duct. ref : SRB&;s manual of surgery,3 rd ed,pg no 576