A first morning sputum is received for culture of acid-fast bacilli. It is digested and concentrated by the N-acetyl-L-cysteine alkali method. Two Sabouraud dextrose slants are incubated in the dark at 35°C with 5-10% CO₂. The smears reveal acid-fast bacilli, but the slants show no growth after 8 weeks. The explanation is:
A) Improper media used
B) Incorrect concentration procedure used
C) Improper specimen submitted
D) Exposure to CO₂ prevents growth
