Final answer:
RNA transcription is repressed when repressors block the binding of RNA polymerase to the promoter.
Step-by-step explanation:
Transcription is repressed when repressors block the binding of RNA polymerase to the promoter. RNA polymerase is the enzyme responsible for transcribing DNA into RNA. When repressors bind to the promoter, they prevent RNA polymerase from binding and initiating transcription, thus blocking the synthesis of RNA.