Question

Of the nrem sleep stages, stage _____ is the longest for people in their early 20s.

Answer 1

The answer for this question is: Stage 2
Stage 2 of the NREM sleep usually happen for about 20 minutes, which cause the body temperature of the subject to drop.
If the subject already enter this stage, it will become a lot harder to be woken up because it almost come nearer to the deep sleep state.