The correct answer is: D. Traffic Collision Avoidance System.
TCAS is a system that helps prevent mid-air collisions between aircraft. It is an independent system that is installed on board aircraft and operates independently of the air traffic control system. TCAS works by continuously monitoring the traffic environment around the aircraft and providing warnings to the flight crew if there is a risk of collision. The flight crew can then take action to avoid the collision.
TCAS is a very effective system and has been credited with preventing many mid-air collisions. It is a mandatory system for all commercial aircraft operating in the United States and many other countries.
The other options are incorrect.
A. Train Collision Advance System is not a real system.
B. Train Complement Accident Software is not a real system.
C. Train Collision Avoidance Software is not a real system.