Answer:
C. dNTPs
Explanation:
dNTP stands for deoxynucleoside triphosphate. They are composed of a sugar, a nitrogenous base and three phosphate groups and they are used in PCR reactions as the monomers of DNA. There are four of them (dATP, dTTP, dGTP and dCTP), each containing a different nitrogenous base (adenine, thymine, guanine or cytosine respectively).
When the DNA polymerase extends the primers, it adds a dNTP complementary to the template strand. If dNTP were not added to the mix, no nucleotides would be available to synthesize new strands and no amplification would happen.