Which of the following best exemplifies a "clue" in the environment?

The choice that stands out as a "clue" in the environment is the sound of humming air. This response highlights how environmental cues can be perceptible through auditory signals, which are crucial in orientation for individuals who may rely on hearing to gather information about their surroundings.

Sounds can convey information about proximity, location, or even activity happening nearby. For instance, the sound of humming air might indicate the presence of air conditioning or machinery, providing context about a space or leading someone to understand their environment better.

Whereas the other options involve more explicit indicators—like a person directing traffic, a written sign, or a marker on a map—the sound of humming air requires interpretation and awareness of the auditory cues that present themselves within a specific setting. This distinction emphasizes the importance of developing a broad range of sensory skills for orientation in navigating environments.