Which base pairing in DNA involves three hydrogen bonds?

• A. A-T
• B. A-C
• C. G-C
• D. T-U

Answer: (C)

Guanine–cytosine pairing involves three hydrogen bonds. The specific interaction between G and C forms three points of contact, making GC pairs stronger and more thermally stable than adenine–thymine pairs, which have two hydrogen bonds. A-T is not the three-hydrogen-bond situation, and A-C is not a standard DNA base pair. T-U is a RNA-related pairing and does not create three hydrogen bonds in DNA context.