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: Dental
In diagnosing the carious lesions, the tooth surface is examined visually. Which of the following is not considered as visual examination? 
Select and explain. 
A. Cavitations, B. Brownish black discoloration of pits and fissures, C. Opacification, D. Softness of the tooth surface
D: Softness of the tooth surface
Answer: D: Softness of the tooth surface 
Explanation: The caries can be detected by 

Visual methods (Cavitation, Chalky appearance of teeth)
Tectile methods (Checking carefully by using an explorer)