The answer would be:
C. Transcription
Here's a little more about gene regulation:
Gene regulation as mentioned already, is the process of turning genes on and off. In multicellular organisms, the different cells have the same DNA in them but through gene regulation, different sets of genes are expressed. The genes that are expressed determine the function and appearance of the cell.
Answer:
C) Transcription
Although gene regulation can occur at any point during gene expression, it most commonly occurs at the level of when the information in a gene’s DNA is transferred to mRNA.
(copied from USATESTPREP)