Strengthen-CE. The correct answer choice is (E)
Because those who are deprived of REM sleep become more irritable, the author concludes that REM sleep relieves stress (the first two sentences in the stimulus are largely inconsequential to understanding this argument). You should immediately notice the strong causal element of the conclusion:
- Cause Effect
Premise: No REM → Increased stress
Conclusion: REM → Stress relief
Answer choice (A): This answer does the exact opposite of what is needed: it weakens the argument by suggesting an alternate cause (general lack of sleep) for the stated effect (irritability). This answer choice is incorrect.
Answer choice (B): This answer choice is entirely irrelevant to strengthening the argument. If anything, it might suggest that REM (which is when people dream) can itself sometimes cause stress, which would weaken the conclusion.
Answer choice (C): By implying the reverse causal connection between REM and stress (stress causes disturbance in REM sleep, not the other way around), this answer choice weakens the argument and is therefore incorrect.
Answer choice (D): Remembering one's dream is inconsequential to the author's argument.
Answer choice (E): This is the correct answer choice. If normally experienced shorter periods of REM sleep are correlated with increased stress, this eliminates some of the alternate causes for increased stress among the test subjects, such as general sleep disturbance and chronic deprivation.