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
Calculus is the: 
Select and explain. 
A. Governing factor., B. Contributing factor., C. Etiological factor., D. Primary factor.
B: Contributing factor.
Answer: B: Contributing factor. 
Explanation: Calculus does not directly irritate the gingiva but it provides a fixed nidus for the continued accumulation of plaque and holds it against gingiva and thus acts as a contributing factor.