Answer:
Thymine
Step-by-step explanation:
Deoxyribonuceic acid (DNA), is the stored form of genetic material in an organism's cell. It is one of the two types of nucleic acid, made up of nucleotide sequences. A nucleotide is a combination of a five-carbon sugar (Deoxyribose in DNA), phosphate group and nitrogenous base.
A DNA molecule consists of two long polynucleotide chains composed of four types of nucleotide subunits (Adenine, Thymine, Guanine, and Cytosine). Each of these chains is known as DNA strand. The nitrogenous bases in DNA align with each other in a manner called base pairing.
Complementary base pairing is the phenomenon whereby in DNA, Adenine (A) always hydrogen bonds to Thymine (T), while Guanine (G) bonds to Cytosine (C) i.e. A-T, G-C . In complementary base pairing, a purine (Adenine and Guanine) always binds to a pyrimidine (Cytosine and Thymine). This pairing is responsible for the double-helical structure of the DNA.