When Kelly was in a passenger plane, he watched as all four engines quit at once and then saw the plane explode. From 5,000 feet in the air, he landed, severely injured, in deep snow in a heavily wooded area. When he regained consciousness several weeks later, he had a stress reaction that lasted for years, and he could never fly again. The factor that probably MOST contributed to his extreme posttraumatic stress reaction was:

Post-traumatic stress disorder.

Explanation:

It is an event that occurs in people who have witnessed or directly experienced a stressful event from the past. When a person finds himself in a dangerous situation, it is natural for him to feel fear. This fear triggers many extremely rapid changes in the body that prepare the person to defend themselves or avoid them. However, with this disorder, this reaction is reversed. People with this disorder feel fear even when they are not in a dangerous situation.

ever since wwii tmthey always did hated each other.