Why is it important for ATC to monitor specific aircraft cruising altitudes?

Answer: B — To prevent mid-air collisions

Monitoring specific aircraft cruising altitudes is crucial for air traffic control primarily to prevent mid-air collisions. By keeping a close watch on the altitudes at which different aircraft are flying, air traffic controllers can maintain safe vertical separation between aircraft in the same airspace. Established altitude assignments help to manage the flow of traffic and reduce the risk of incidents in busy airspace, where multiple aircraft may be operating simultaneously. This vertical spacing is vital for avoiding potential conflicts and ensuring the safety of all flights. While effective communications, aircraft classification, and passenger comfort are important aspects of air traffic management, they do not directly address the critical need for maintaining safe distances between aircraft in flight, which is paramount for accident prevention.