Comprehensive and Detailed Explanation:
PE Room Design: ASHRAE Standard 170, Section 7.2.2, requires positive pressure with supply air from ceiling diffusers (HEPA-filtered) and return/exhaust low on the sidewall to maintain airflow from clean to less clean areas (e.g., towards the entrance).
Option Analysis:
A: Toilet exhaust is separate, not the primary return.
B: Floor placement is less common and less effective.
C: Anteroom return doesn't control room airflow.
D: Correct-low sidewall near entrance optimizes airflow.