The correct option is B Promoter
Introns and exons are formed in a process called post-transcriptional modification. This takes place after transcription is carried out. Therefore before transcription, they are found combined together and are collectively known as the RNA coding region or the Gene. The terminator sequence is also required for the RNA polymerase to stop copying things down and hence included in the transcription unit, although it does not form a part of the structural or core Gene. The promoter however, is present on the strand just to help RNA polymerase recognise the transcription unit. In some cases still, RNA polymerase will be bound to the promoter and another part of the transcription unit, like a repressor, will be blocking its activity, as is the case in the Lac Operon.