Final answer:
Inspiration is an active process during which the muscles of respiration contract, thereby enlarging the thoracic cavity and reducing the pleural pressure, creating a negative pressure that facilitates the inflow of air.
Step-by-step explanation:
Inspiration is a process related to the mechanism of breathing, specifically when air is taken into the lungs. During this phase, the thoracic cavity expands as the muscles involved in breathing, such as the diaphragm and intercostal muscles, contract. This contraction enlarges the chest cavity and reduces the intrapleural pressure within the pleural space to an even lower negative pressure relative to atmospheric pressure. Therefore, the correct answer is Inspiration is a/an active process causing a negative pressure in the pleural space, which corresponds to option B. Active/negative.