What physical condition may prevent a person from swimming well?

The correct choice emphasizes that multiple physical conditions can significantly impact a person's ability to swim effectively. Hypoglycemia refers to low blood sugar levels, which can lead to dizziness, weakness, and confusion, all of which can hinder swimming performance. Dehydration can cause fatigue, cramping, and decreased coordination, making it difficult to swim efficiently. Hypothermia, which occurs when the body loses heat faster than it can produce it, can impair muscle function and cognitive abilities, rendering swimming unsafe. Exhaustion, which can arise from overexertion or inadequate rest, can severely diminish strength and stamina, increasing the risk of fatigue in the water.

In contrast, while asthma can affect breathing, many individuals with well-managed asthma can swim effectively. Overhydration is less common and typically does not create immediate adverse effects on swimming ability, although it can lead to complications in extreme cases. Cardiac fatigue is generally a broader term and may not directly correlate to acute conditions affecting swimming performance. The collective impact of the specific conditions in this answer underscores their direct link to swimming competency, making it the correct choice.