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
Yard-stick of detection in Snyder's test is: 
Select and explain. 
A. Acid formation, B. pH change, C. Count of microorganisms, D. Enamel solubility
B: pH change
Answer: B: pH change 
Explanation: Snyder's test uses Bromocresol green as an indicator, which is blue-green at pH 5.4 or above and turns yellow at pH 3.8 or less. 
The "critical pH" for enamel dissolution is 5.4-5.5.
Therefore, it would be more appropriate to use an indicator such as Bromocresol purple, which is purple at pH 6.8 and yellow at pH 5.2.

Soben Peter 5th edition
Page number  434