In prokaryotic cells, regulator proteins bind to a section of DNA called a/an A)chromatin
B)repressor***
C)promoter
D)operon
“*** is my answer”

C) Promoter

Explanation:

Gene expression is the process of synthesizing RNA from a gene (transcription), and subsequently, proteins from mRNA (translation). In both prokaryotic and eukaryotic cells, gene expression is controlled at the transcriptional level, which is regulated by certain proteins called transcription factors. Transcription factors are proteins that regulate the synthesis of a protein from a gene.

Transcription factors regulate the progression of transcriptional process by binding to a regulatory region on the DNA sequence about to be transcribed called PROMOTER. The promoter region is a DNA sequence contained in the OPERON. This binding influences the binding of the transcription enzyme, RNA polymerase in order for transcription to start.

i think that the best answer would be c.

tell me if im wrong : )