In Bacteria, the Biosynthetic Routes for Proline and Arginine Diverge $\delta$

In bacteria, the biosynthetic routes for proline and arginine diverge when glutamate is N-acetylated for arginine synthesis. Which of the following explains why acetylation is required for arginine synthesis but not proline synthesis?

A) acetylation alters the pK_a of the amine group
B) acetylation prevents reduction of the amine group in N-acetylglutamate- $\delta$ -semialdehyde
C) acetylation activates the amine group for synthesis of the guanidine group of arginine
D) acetylation prevents the cyclization of N-acetylglutamate- $\delta$ -semialdehyde
E) none of the above