Final answer:
The DNA sequence amplified in a PCR reaction is specified by the primers, which are short DNA sequences complementary to the target DNA. Taq polymerase extends the new strands during the PCR cycles.
Step-by-step explanation:
The DNA sequence amplified in a PCR reaction is specified by C. The primers. These primers are short sequences of DNA that are designed to be complementary to the specific segments of the target DNA strands. The PCR process includes repeated cycles of heating and cooling to allow for the denaturation of the DNA double helix, annealing of the primers to their complementary sequences, and extension of the new DNA strands by Taq polymerase. Taq polymerase is a DNA polymerase that remains functional at high temperatures and thus is ideal for the PCR process. Functions such as splice sites, promoters, stop codons, and the physical ends of DNA do not determine the specificity of the PCR amplification.