The Trp operon in Escherichia coli encodes the components necessary for tryptophan biosynthesis. In the presence of the amino acid in a bacterium, …

A) the tryptophan operator is bound to the tryptophan repressor.
B) the tryptophan repressor is bound to bacterial RNA polymerase.
C) the expression of the tryptophan repressor is shut off.
D) the operon genes are expressed.
E) All of the above.