Which of the following is a factor that can increase susceptibility to oxygen toxicity?

Overheating during a dive is a significant factor that can increase susceptibility to oxygen toxicity. When a diver becomes overheated, it can lead to an increased metabolic rate, which subsequently raises the body's consumption of oxygen. This increase in oxygen consumption heightens the risk of experiencing toxic effects from the elevated partial pressure of oxygen present at certain depths during diving.

In contrast, low humidity, deep diving on air, and a healthy diet do not directly contribute to an increase in oxygen toxicity susceptibility in the same way. While environmental conditions like humidity can affect dive comfort, they are not primary factors in oxygen toxicity. Likewise, deep diving on air does present risks, particularly due to nitrogen narcosis and decompression sickness, but not specifically in relation to oxygen toxicity unless one is diving at high partial pressures of oxygen, which typically occurs when using enriched air. A healthy diet is important for overall health and physical performance but does not influence oxygen toxicity directly.