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
Supragingival plaque undergoes which of the following changes with time? 
Select and explain. 
A. Plaque mass decreases, B. Plaque microflora becomes more gram positive, C. Plaque microflora becomes gram negative, D. Plaque microflora becomes predominantly spirochetal
C: Plaque microflora becomes gram negative
Answer: C: Plaque microflora becomes gram negative 
Explanation: None