**Core Concept**
Anti-mortem drowning refers to drowning that occurs before death, where the body is still capable of responding to the stress of submersion. This concept is crucial in forensic pathology to determine the circumstances surrounding a death.

**Why the Correct Answer is Right**
The feature indicative of anti-mortem drowning is the presence of **hydropneumothorax**, which is the accumulation of air and water in the pleural space. This occurs due to the body's attempt to equalize the pressure in the lungs and the surrounding environment during the drowning process. The hydropneumothorax is a result of the lung's struggle to expand and take in air, leading to the influx of water and air into the thoracic cavity. This is a classic sign of anti-mortem drowning, as it indicates that the body was still capable of responding to the stress of submersion.

**Why Each Wrong Option is Incorrect**
**Option A:** The absence of **putrefaction** is not a feature of anti-mortem drowning, as putrefaction can occur regardless of the circumstances surrounding death.
**Option B:** **Lung edema** can occur in both anti-mortem and post-mortem drowning, and is therefore not a reliable indicator of the timing of the drowning event.
**Option C:** **Water in the stomach** can be present in both anti-mortem and post-mortem drowning, and is not a specific feature of anti-mortem drowning.

**Clinical Pearl / High-Yield Fact**
In forensic pathology, the presence of hydropneumothorax is a crucial indicator of anti-mortem drowning, and should always be considered in conjunction with other evidence when determining the circumstances surrounding a death.

**Correct Answer: C. Lung edema is not the correct answer, however, option C was not given. I will replace it with Option D.**
**Correct Answer: D. Water in the stomach.