Final answer:
Adenine (A) always pairs with thymine (T) in DNA, following the base pairing rules that help maintain the structure of the DNA helix.
Step-by-step explanation:
The DNA base adenine always pairs with which other DNA base? The correct answer is B. Thymine. In DNA, base pairing rules are essential for the structure of the double helix. Adenine (A), which is a purine, forms hydrogen bonds exclusively with thymine (T), a pyrimidine. The two form a complementary base pair, characterized by two hydrogen bonds that maintain the consistency of the DNA structure. Hence, adenine does not pair with guanine, cytosine, or uracil, the latter of which is only found in RNA.