Trachea is the tube that connects the lungs to source of air outside. It is also called the windpipe, connecting the pharynx to the lungs and allowing the passage of air. It is about 4 inches long and less than an inch in diameter.
Trachea is not kept open by air pressure.
Trachea is not reinforced with any non-collapsible bone structure.
Trachea is not kept open with any special muscles either.
Therefore, options A, C and D are incorrect.
Trachea is supported by circular tough cartilaginous rings (about 20 of them) that keep it open. Trachea finally divides into branches called bronchi, which lead to the lungs. The trachea also widens and lengthens with each breath (returning back to the normal state), facilitating air movement.
Therefore, option (B) is correct.