Final answer:
A smoke stack is a point source of air pollution identified by the nurse, which refers to a fixed location where pollutants are emitted.
Step-by-step explanation:
The nurse has identified a smoke stack as a point source of air pollution. A point source has a specific, single location from which pollutants are released, such as a factory's smoke stack. This is different from area sources or nonpoint sources like cars and trucks, which are considered mobile sources because they can move and emit pollutants over a wider area. In contrast to point sources like a smoke stack, nonpoint sources of pollution, such as the number of vehicles or ground ozone levels, refer to pollution that comes from multiple dispersed sources.