The correct answer is C) Never remove the line from the rocket. The primary reason for this is safety. When testing a line throwing gun, the line should remain attached to the rocket or projectile at all times. Removing the line could cause the rocket to fire in an uncontrolled manner, posing a serious safety hazard. Additionally, the line helps stabilize the trajectory of the projectile, ensuring it reaches the target safely. The other answer choices are incorrect because they do not address the key safety concern of keeping the line attached. Firing the gun at a 90-degree angle is not a necessary precaution, and wearing asbestos gloves is an outdated and unnecessary safety measure for this type of equipment.