Passage Summary: Since people become irritable when they don't get the kind of sleep where dreaming happens, that specific sleep stage must be responsible for relieving stress.

Conclusion: REM sleep serves to reduce the stresses encountered during daily life.

Reasoning: Dreams occur only during REM sleep, and individuals who are consistently deprived of this specific sleep stage exhibit irritability while awake.

Analysis: The argument moves from a correlation (lack of REM and irritability) to a causal claim (REM causes stress relief). To strengthen this, we need to bolster that causal link. Look for an answer that suggests irritability is a direct result of stress, or perhaps one that shows that other stages of sleep do not provide this same benefit. Eliminating an alternative cause for the irritability would also effectively support the author's conclusion.