Final answer:
A PCT must wear an N95 respirator as the most crucial piece of PPE when caring for a patient with pulmonary tuberculosis to prevent inhaling airborne bacteria.
Step-by-step explanation:
A Patient Care Technician (PCT) preparing to care for a patient with pulmonary tuberculosis should put on an N95 respirator before entering the patient's room. Tuberculosis (TB) is an airborne disease caused by the bacterium Mycobacterium tuberculosis, and it can be easily inhaled. Therefore, the most crucial piece of personal protective equipment (PPE) in this scenario is the N95 respirator, which is designed to filter airborne particles efficiently and prevent the inhalation of the bacteria that cause TB.