This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oral cavity, Subject name: Surgery
Areas of carcinoma of oral mucosa can be identified by staining with: 
Select and explain. 
A. 1% zinc chloride, B. 2% silver nitrate, C. Gentian violet, D. 2% toluidine blue
D: 2% toluidine blue
Answer: D: 2% toluidine blue 
Explanation: Toluidine Blue Toluidine blue is a basic metachromatic dye with high affinity for acidic tissue components, thereby staining tissues rich in DNA and RNAQ. Wide applications both as vital staining in living tissues and as a special stain used in vivo to identify dysplasia and carcinoma of the oral cavityQ.