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 sample of human DNA is subjected to increasing temperature until major portion of the sample melts. A small portion of the DNA requires even higher temperature compared to rest of the sample. This may be having higher content of 
Select and explain. 
A. Adenine and guanine, B. Cytosine and guanine, C. Cytosine and thymine, D. Adenine and thymine
B: Cytosine and guanine
Answer: B: Cytosine and guanine 
Explanation: C and G have three hydrogen bonds compared to A and T which have two hydrogen bonds. Hence C-G base pair rich, DNA has high melting temperature.