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
A 4 year old female child complains of weakness and pain in joints. Her parents are known case of sickle cell trait. Hb electrophoresis reveal HbS pattern. This disease occurs because of which base alteration? 
Select and explain. 
A. CTC → CAC in DNA, B. GAG → GUG  in DNA, C. CTC → CAC  in  RNA, D. GAG → CAC  in RNA
A: CTC → CAC in DNA
Answer: A: CTC → CAC in DNA 
Explanation: The occurrence of the disease sickle-cell anemia due to a single base alteration (CTC + CAC in DNA, and GAG + GUG in RNA) is a classical example of the seriousness of mutations.
Satyanarayana- Biochemistry, 3rd edition, pg-549