**Core Concept**
The question is testing the understanding of the physiological effects of alcohol withdrawal, specifically the most common feature. Alcohol withdrawal occurs when an individual who has been consuming alcohol regularly suddenly stops or significantly reduces their intake, leading to a rebound effect on the body's physiological systems.

**Why the Correct Answer is Right**
The most common feature of alcohol withdrawal is tremors. This is due to the depletion of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter in the brain. As alcohol consumption decreases, the levels of GABA decrease, leading to an increase in excitatory neurotransmitters such as glutamate. This imbalance disrupts the normal functioning of the nervous system, resulting in symptoms such as tremors. The tremors are usually seen in the hands and fingers and can progress to more severe symptoms such as seizures and delirium tremens if left untreated.

**Why Each Wrong Option is Incorrect**
* **Option A:** Sweating is a possible symptom of alcohol withdrawal, but it is not the most common feature. Sweating is often seen in conjunction with other symptoms such as tremors and anxiety.
* **Option B:** Anxiety is a common symptom of alcohol withdrawal, but it is not the most common feature. Anxiety can range from mild to severe and can be accompanied by other symptoms such as tremors and sweating.
* **Option C:** Insomnia is a possible symptom of alcohol withdrawal, but it is not the most common feature. Insomnia can occur due to the disruption of the body's normal sleep-wake cycle caused by the withdrawal of alcohol.

**Clinical Pearl / High-Yield Fact**
The symptoms of alcohol withdrawal can be remembered using the acronym **FIND**: Flushing, Insomnia, Nausea, and Diaphoresis (sweating). However, the most common feature is often tremors, which is why it is essential to identify and manage tremors promptly.

**Correct Answer:** C.