Rna polymerase opens the double helix at the promoter.
a. initiation
b. elongation
c. termination

Initiation.

Explanation:

Transcription may be defined as the process of formation of RNA molecule from the DNA template with the help of the enzymes and transcription factors. The three important steps of transcription are initiation, elongation and termination.

The RNA polymerase is an enzyme that plays an important role in the transcription. During initiation process, RNA polymerase binds to the sigma factor. The binding of RNA switches the DNA from the closed complex to the open complex. The DNA separates from its strands for the formation of unwound DNA and leads to the formation of transcription bubble.

Thus, the correct answer is option (a).