Attenuation in the Trp Operon of E. Coli

Attenuation in the trp operon of E. coli:

A) can adjust transcription of the structural genes upwards when tryptophan is present.
B) can fine-tune the transcription of the operon in response to small changes in Trp availability.
C) is a mechanism for inhibiting translation of existing (complete) trp mRNAs.
D) results from the binding of the Trp repressor to the operator.
E) results from the presence of short leader peptides at the 5' end of each structural gene.