I didn't get this question, please explain.

16. Besides the repression/depression control of tryptophan operon, the second level of regulation is known as attenuation. The presence of two tryphotophan codons within the trp L controls this phenomenon. The presence of tryptophan-charged t RNArp Causes the premature termination of transcription, yields a 140 nucleotide long leader sequence transcript. By site directed mutagenesis, the two UGC trp codons of the trp L sequence were modified to CGG, arginine codon (arg). Which of the following amino acids would be able to restore the attenuation control of trp operon? (a) Tryptophan alone (b) Arginine alone (c) Both (a) and (b) (d) Neither (b) nor (a)