There are 4 nucleotides in DNA molecules: guanine (G), cytosine (C), adenine (A), and thymine (T).
Guanine and cytosine bind together (G-C), and adenine and thymine bind together (A-T). These are the only two possible binds in a DNA molecule.
Answer A has a guanine and adenine bond (G-A), which is impossible.
Answer B has a cytosine and cytosine bond (C-C), which is impossible.
Answer D has a cytosine and thymine bond (C-T), which is impossible.
Through the process of elimination, the answer is C.
