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
A punch biopsy shows carcinoma rectum with fixed mass. X-ray chest normal, which of the following is LEAST useful investigation 
Select and explain. 
A. Rigid protoscope, B. Barium enema, C. CT chest, D. MRI-abdomen and pelvis
A: Rigid protoscope
Answer: A: Rigid protoscope 
Explanation: Rigid protoscope is of least significance in carcinoma rectum with fixed mass