Answer 1: None.
Well they are rather interested in preventing the bulb from burning out in the first place. If they have to change the lightbulb, they'd probably refer it to clinicians.
Answer 2: A whole community.
Public health professionals are interested in improving lives through the organized efforts of the community.
Answer 3: None.
They are not interested in changing a single lightbulb. Tell them if multiple bulbs are out, they'll investigate the cause epidemiologically.
