Answer:
Cytosine
Step-by-step explanation:
DNA come in base pairs. According to the Chargaff's rule on base pairs, DNA base pairs come in a 1:1 ratio. The base pair of guanine is cytosine (Adenine pairs with Thymine). The 1:1 ratio indicates that for every 1 guanine there is 1 cytosine. So this means that there is an equal amount of guanine and cytosine.