Which of the following correctly pairs the bases within the DNA double helix?

In the structure of DNA, the bases pair specifically according to the rules of complementary base pairing. Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G). This means that the correct pairing involves A with T and C with G.

The choice indicating A-T and G-C correctly describes this fundamental pairing principle, as A and T form two hydrogen bonds with each other, while C and G form three hydrogen bonds. This complementary pairing is critical for the stability of the DNA double helix and plays an essential role in processes such as DNA replication and transcription.

In the other options, the pairs listed do not align with the established base pairing rules. For example, A-U is a pairing found in RNA, not DNA. A-G and T-C do not represent any known or viable base pairing within the context of a DNA molecule. Thus, the answer that describes the pairing of A-T and G-C accurately reflects the correct complementary interactions in the DNA structure.