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
Materia alba 
Select and explain. 
A. Lack microorganisms, B. Has an irritating effect on gingiva, C. Has a regular internal pattern, D. Is only salivary protein and food debris
B: Has an irritating effect on gingiva
Answer: B: Has an irritating effect on gingiva 
Explanation: None