Before ARF Transcription Factors Can Trigger Auxin-Induced Gene Expression,what Must

Before ARF transcription factors can trigger auxin-induced gene expression,what must happen?

A) Auxin binds to ubiquitin,a degradation tag.
B) Auxin degrades Aux/IAA proteins which repress ARF transcription factors.
C) Auxin binds to TIR1,an auxin receptor.
D) Auxin must bind to the ARF transcription factor.
E) Ubiquitin must destroy TIR1 to release Aux/IAA proteins.