Question

according to the rules of complementary base pairing in nucleic acids, cytosine would pair with the base

guanine.
uracil.
thymine.
adenine.
cytosine.

Explanation:

In nucleic acids, according to the rules of complementary base - pairing, cytosine (C) always pairs with guanine (G). Adenine (A) pairs with thymine (T) in DNA and with uracil (U) in RNA.

Answer:

A. guanine