This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
The best investigation for colorectal carcinoma - 
Select and explain. 
A. Exfoliative cytology, B. Air contrast barium enema, C. Ultrasound, D. Colonoscopy and biopsy
D: Colonoscopy and biopsy
Answer: D: Colonoscopy and biopsy 
Explanation: None