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: Biochemistry
Transition mutation of GATCCT is: 
Select and explain. 
A. GGTCCT, B. GTTCCT, C. GABCCT, D. GrUGGT
A: GGTCCT
Answer: A: GGTCCT 
Explanation: A i.e. G G T C C T