Answer:
The correct answer is B.
Explanation:
Adenine and guanine are purine bases, thymine and cytosine are pyrimidines which make up the structure of the DNA. They are not tautomers. They can however get involved in tautomerism which is the transfer of protons and electrons between chemical compounds that are usually structurally isomers. So the answer is B.
I hope this helps.
