Which of the following can make you unable to sustain efforts in recreational diving?

Inadequate rest can significantly impair your ability to sustain efforts while recreational diving. When divers do not allow their bodies sufficient time to recover, fatigue sets in, which can affect physical performance, decision-making skills, and overall safety underwater. It's essential for divers to be well-rested, as tiredness can lead to slower reaction times, increased exertion, and a greater likelihood of making errors. Adequate rest ensures that physical and mental capabilities are at their best, which is crucial in a potentially stressful diving environment.

Other factors, such as extreme hydration, visual impairments, and overtraining, may impact a diver's experience, but they do not universally impair the ability to sustain effort as consistently and directly as inadequate rest does.