An extremely loud noise awakens you; you emerge from sleep confused and do not remember the noise. You were most likely in which stage of sleep.
a. Stage 1
b. Stage 2
c. REM
d. Stage 4
e. Twilight Sleep
2 answers
And your choice is?
May I suggest you read your text materials, or, failing that, consult this:
http://www.sleepdex.org/stages.htm
http://www.sleepdex.org/stages.htm