The correct answer is (d). Guanine is a purine base.
Purine bases are nitrogenous bases that are found in DNA and RNA. They are composed of two rings, a pyrimidine ring and an imidazole ring. The purine bases are adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine and guanine are complementary bases, meaning that they pair together in DNA. Cytosine and thymine are also complementary bases.
Purine bases are essential for the structure and function of DNA and RNA. They are also involved in the regulation of gene expression.
(a) Thymine is a pyrimidine base. It is complementary to adenine.
(b) Cytosine is a pyrimidine base. It is complementary to guanine.
(c) Uracil is a pyrimidine base. It is complementary to adenine in RNA.