This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urology, Subject name: Surgery
Most common site for carcinoid tumor 
Select and explain. 
A. Appendix, B. Liver, C. Stomach, D. Rectum
A: Appendix
Answer: A: Appendix 
Explanation: Carcinoid tumour arise from the enterochromaffin cells (Kulchitsky cells) found in the crypts of Lieberkuhn. These cells are capable of APUD (Amine precursor uptake and Decarboxylation) and can secrete vasoactive amines like 5- HT, 5-HIAA, 5-HTP; tachykinins, peptides (chromogranins)and PGs. It commonly occurs in appendix (45%), ileum (25%) and rectum (15%). Other (15%) sites are--other pas of GIT (including pancreas and biliary tract), bronchus and testis.Reference: page 877 SRB's manual of surgery 5th edition