PT48, S4, Q2 Sleep research has demonstrated that sleep is

[aileenann]

2. (E)
Question Type: Strengthen the Argument
The argument concludes that REM sleep relieves stress. The argument’s reasoning is based on an assumption that the correlation between the deprivation of REM and irritability is a causal relationship. However, causal conclusions are often problematic, and this one is no exception. This causal conclusion needs some additional assumptions to rule out other factors or a reverse causal relationship (i.e. perhaps the irritability causes deprivation of REM sleep rather than the reverse.). (E) provides another example that indicates that REM sleep relieves stress and rules out interference by other factors.

(A) weakens the argument because it indicates that all sleep, rather than just REM sleep, may relieve stress.
(B) weakens the argument because it indicates that dreams experienced during REM sleep may actually cause stress.
(C) weakens the argument because it suggests the opposite causation described in the argument itself.
(D) is out of scope.