Why are transcriptional regulator proteins necessary?

Why are transcriptional regulator proteins necessary?

A. The transcriptional regulator proteins keep the apparatus from being degraded by enzymes.

B. The basal transcriptional apparatus will not bind to the promoter without them.

C. The basal transcriptional apparatus will repress transcription without them.

D. The basal transcriptional apparatus can only produce minimal levels of transcription without them