Question

the nitrogen base that is complementary to thymine is

a adenine

b uracil

c guanine

d cytosine

Explanation:

In DNA, nitrogen - base pairing follows specific rules. Adenine (A) pairs with thymine (T) through two hydrogen bonds. Guanine (G) pairs with cytosine (C) through three hydrogen bonds. Uracil (U) is found in RNA and pairs with adenine (A) in RNA. Since the question is about DNA (as thymine is a DNA - specific base), the complementary base to thymine is adenine.

Answer:

A. adenine