Answer:
Adenine.
Step-by-step explanation:
DNA is present in the living organism as the hereditary material that can be transmitted to the next generation. The DNA consist of four nitrogenous bases, phosphate molecule and the pentose sugar.
The DNA shows complementary with each other by showing bonding with specific nitrogenous bases. Cytosine binds with guanine and adenine binds only with thymine with two hydrogen bonds. Thymine shows the complement base with adenine.
Thus, the answer is adenine.