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
Neurological menifestations of fluorosis occur , when the duration of ingestion is: 
Select and explain. 
A. 10 years, B. 15 years, C. 20 years, D. 25 years.
D: 25 years.
Answer: D: 25 years. 
Explanation: The fluoride dosage necessary to produce pathological skeletal fluorosis is estimated to be 20-80 mg/day for a period of 10 to 20 years. In India, it is most commonly seen in Punjab. Neurological Manifestations of fluorosis occur if the duration of ingestion is more than 20 years.