**Core Concept**
Post-traumatic stress syndrome (PTSD) is a psychological disorder that occurs in individuals who have experienced or witnessed a traumatic event, leading to symptoms of anxiety, depression, and flashbacks. The underlying concept being tested is the relationship between traumatic events and the development of PTSD.

**Why the Correct Answer is Right**
PTSD is characterized by the inability to process and cope with the traumatic event, resulting in the development of intrusive memories, avoidance behaviors, and increased arousal. Major life-threatening events, such as combat, natural disasters, or physical assault, can trigger the onset of PTSD. The amygdala, a key structure in the brain's emotional processing center, plays a crucial role in the development of PTSD. The amygdala's hyperactivity in response to traumatic stimuli can lead to the formation of traumatic memories and the associated symptoms of PTSD.

**Why Each Wrong Option is Incorrect**
**Option A:** A head injury alone is not sufficient to cause PTSD, although it may contribute to the development of other psychological disorders, such as post-concussive syndrome.
**Option B:** Cardiovascular disease is not directly related to the development of PTSD, although individuals with PTSD may have an increased risk of developing cardiovascular disease due to chronic stress and anxiety.
**Option C:** Minor stress is not typically associated with the development of PTSD, which requires exposure to a significant traumatic event.

**Clinical Pearl / High-Yield Fact**
PTSD is a treatable condition, and early intervention with cognitive-behavioral therapy (CBT) and medication can significantly improve symptoms and quality of life.

**✓ Correct Answer: D. Major life threatening events**