Which of the following is a symptom of hyperglycemia?

The correct choice is A, as symptoms of hyperglycemia, or high blood sugar, commonly include flushed skin and increased thirst. When blood glucose levels rise beyond the normal range, the body attempts to manage this excess sugar by drawing water from cells, leading to increased thirst, a condition known as polydipsia. The skin may also appear flushed due to dehydration and altered circulation as a result of high glucose levels affecting fluid balance.

In contrast, other symptoms noted in the incorrect choices reflect different medical conditions. Cold, clammy skin and hallucinations are typically associated with hypoglycemia, or low blood sugar, where the body's glucose supply is insufficient for normal function. Symptoms like rapid heartbeat and anxiety can occur in both hyperglycemia and hypoglycemia, but they are more indicative of hypoglycemia when accompanied by other specific manifestations. Lastly, while frequent urination is indeed a symptom of hyperglycemia, muscle weakness is less characteristic and may relate to other issues such as electrolyte imbalances or overall dehydration.