Which modification occurs in beta-D-glucose to form N-acetylglucosamine (NAG)?

• A. Addition of a carboxyl group at C4.
• B. Addition of a phosphate group at C1.
• C. Replacement of the hydroxyl group at C2 with an N-acetyl group.
• D. Replacement of the hydroxyl group at C3 with a methyl group.

Answer: (C)