In negative regulation, a. the gene is never transcribed. b. the gene is always transcribed. c. the binding of an activator stimulates transcription. d. transcription can be turned off when a repressor binds to the dna near the promoter. e. a transcription factor is required in order for the gene to be transcribed.

The correct answer is d: transcription can be turned off when a repressor binds to the DNA near the promoter.
The repressor is a protein which prevents a gene from being expressed (inhibits transcription from occurring). Near the promoter, there is a site called the operator, which is the binding site for the repressor. When the repressor binds, RNA polymerase is prevented from binding to the promoter and initiating transcription. Gene expression is then turned off.

Carbon monoxide is the answer: )