The following schematic drawing represents the activation of transcription for a eukaryotic gene (gene X). Indicate what component (A to D) in the drawing corresponds to each of the following. Your answer would be a four-letter string composed of letters A to D only, e.g. ADBC.

( ) Mediator
( ) cis-Regulatory sequence
( ) A general transcription factor
( ) "Spacer" DNA that may encode lncRNAs