The typical treatment for people with phenylketonuria is a diet low in phenylalanine.If one were to design a gene therapy for this disease,which would be the most promising approach?

A) Doing nothing.
B) Engineering a gene that codes for the enzyme that converts tyrosine to phenylalanine
C) Engineering a gene that codes for the enzyme that converts homogentistic acid to phenylalanine
D) Reducing the level of protein synthesis from a gene that codes for the enzyme that converts phenylalanine to tyrosine
E) Engineering a gene that codes for the enzyme that converts phenylalanine to tyrosine