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
Variation of eruption of secondary dentition can be: 
Select and explain. 
A. 4-5 months., B. 6-7 months., C. 12-18 month., D. Variations in eruption of secondary dentition is less frequent.
C: 12-18 month.
Answer: C: 12-18 month. 
Explanation: None