What defines drowning?

The correct choice highlights that drowning is fundamentally characterized by impaired respiratory function following immersion in liquid. This defines the primary biological consequence of drowning, which is the inability to breathe effectively due to the airway being submerged in a liquid, often leading to respiratory distress or failure.

When a person is submerged in water, the body's ability to exchange gases is compromised, leading to a lack of oxygen and the potential for carbon dioxide buildup. This can occur whether the individual is conscious or unconscious, and the loss of consciousness may be a result of this impaired respiratory function rather than the defining criteria of drowning itself.

Although the other options mention relevant aspects related to water immersion, they do not encapsulate what drowning fundamentally is. Loss of consciousness due to lack of oxygen is a consequence of drowning rather than a definition. Similarly, while submersion may lead to temperature loss, this is not a defining characteristic of drowning as it relates more to hypothermia than respiratory distress. The concept of loss of breath control in open water is also a consequence but does not specifically define the medical condition of drowning itself. Therefore, the definition provided in the correct answer is the most accurate representation of what constitutes drowning.