In a Single PCR Cycle Consisting of 15 Seconds at 94°C

In a single PCR cycle consisting of 15 seconds at 94°C, 30 seconds at 50°C, and 1 min at 72°C, what is happening in the step run at 50°C?

A) DNA polymerase is being inactivated.
B) DNA polymerase is extending new DNA from the primers.
C) Primers are being denatured.
D) Primers are annealing to the DNA to be amplified.
E) The DNA to be amplified is being denatured.