The correct option is B Transcription is blocked
Repressors are proteins that prevent transcription and thus, are said to take negative control of the respective structural genes. When lactose concentration in the medium is low, the repressor binds to the operator in such a way that RNA polymerase is prevented from binding to the promoter. This prevents transcription of the structural genes by RNA polymerase. Thus, repressors ensure that transcription of the genes happens only when required. In the absence of lactose, the enzymes to digest it would not be required and hence, transcription is prevented.