The difference between insomnia and sleep apnea is that _____

A) sleep apnea affects primarily the elderly, whereas insomnia is characteristic of children
B) insomnia is treatable but sleep apnea is not
C) sleep apnea is a precursor to narcolepsy, whereas insomnia is not
D) insomnia is often characterized by sleeplessness, whereas sleep apnea is characterized by breathing difficulties

Answer: D