What component prevents the AIM-120 rocket motor from becoming propulsive?

The correct answer is the thermally initiated venting system. This system is critical for preventing the AIM-120 rocket motor from becoming propulsive when it's not intended to be in operation. It is designed to dissipate heat generated within the rocket motor, ensuring that the propellant does not reach the ignition temperature. By releasing pressure and heat at certain thresholds, the system effectively manages the thermal environment of the motor, preventing unintended ignition.

The other components listed do not serve the same purpose. Pressure release valves are typically used for controlling the internal pressure of a system but do not specifically function to prevent motor propulsion by managing temperature. The cooling fin system may contribute to heat management in a broader sense, but alone, it does not prevent propulsion. Stabilization components are involved in ensuring that the missile maintains proper flight characteristics, but they do not directly affect the readiness or ability of the motor to ignite.