The question is not complete since it does not provide the options to make the analogy, here are the options:
A . rest
B. snoring
C . alarm clock
D. quiet
E . nighttime
The words treaty and war have meanings that might be considered opposite, therefore the required analogy for the word sleep most represent an opposite concept, the words "rest, snoring, quiet and nighttime" are directly connected to the word sleep, which makes the word alarm clock the best option, besides the alarm clock keeps you away from sleeping.
The tone of The Secret Garden is both dark and hopeful so B. Since they are both abused but sort out these issues which give them hope and makes them well... hopeful. I hope this helps!