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: Medicine
Nucleotide repeat in Spinocerebellar ataxia type 6. 
Select and explain. 
A. CAG, B. CGG, C. GAA, D. CTG
A: CAG
Answer: A: CAG 
Explanation: Fragile X - CGG
Freidrich ataxia - GAA
Myotonic dystrophy - CTG