How can you know if carbon monoxide is present?

Carbon monoxide (CO) is a colorless, odorless gas, which makes it quite dangerous because it cannot be detected by the senses. One of the primary ways to identify the presence of carbon monoxide is through the context and source of potential exposure. The correct choice notes that the presence of running cars in poorly ventilated areas is a significant indicator of carbon monoxide buildup. When vehicles are running, especially in enclosed spaces like garages or poorly ventilated areas, they can release carbon monoxide as part of their exhaust.

This context is essential for recognizing the risk factors associated with carbon monoxide exposure. Other incorrect choices emphasize aspects that do not apply to CO detection. For instance, CO has no distinctive smell, which rules out the choice that suggests it can be detected this way. A fire alarm typically responds to smoke or fire, not specifically to carbon monoxide, and visual cues like discolored air are not reliable indicators for this invisible gas. Thus, recognizing the danger associated with certain environments, such as the proximity to running vehicles in confined spaces, is critical for awareness and safety.