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
Because of the confounding factors, additional criteria have been developed by the U.S. public health service for pit-and-tissue caries diagnosis. Which one of the following is NOT a factor of these criteria? 
Select and explain. 
A. Softening at the base of the pit or fissure, B. Opacity surrounding the pit or fissure, C. Softening enamel that may be flaked away by the explorer, D. Discoloration of pit and groves, limited to the depth of the fissure or pit.
D: Discoloration of pit and groves, limited to the depth of the fissure or pit.
Answer: D: Discoloration of pit and groves, limited to the depth of the fissure or pit. 
Explanation: None