**Core Concept**
Run-amok is a psychiatric condition characterized by sudden, violent, and aggressive behavior, often in response to a perceived threat or stressor. This phenomenon is often associated with tropical degeneration of the brain, particularly in Southeast Asian populations.

**Why the Correct Answer is Right**
The correct answer is related to the use of a specific substance that can cause this condition. The substance is known to cause a sudden release of catecholamines, leading to an intense emotional response and aggressive behavior. This is due to the inhibition of the enzyme monoamine oxidase (MAO), which breaks down these neurotransmitters. The substance in question is a plant-based product that has been used in traditional medicine for centuries.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not directly associated with the sudden onset of aggressive behavior.
* **Option B:** This option is incorrect because it does not have a direct link to the tropical degeneration of the brain.
* **Option C:** This option is incorrect because it is not a known cause of run-amok behavior.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that run-amok behavior is often associated with the use of a specific plant-based product that contains a substance that inhibits MAO. This knowledge can help clinicians identify the underlying cause of aggressive behavior and provide appropriate treatment.

**Correct Answer: B. Betel nut.**