The correct answer is sentence (5).
A sentence fragment means that it is only a part of a sentence; it is not complete. Given that it is incomplete, the fragment, aka subordinate/dependent sentence, has to be part of a larger, independent sentence, in order to make any sense. So if you combined sentence (5) with another one, it wouldn't be a fragment anymore.
Happiness comes now and then,
Were not sure when,
But when its here enjoy every minute of it,
Because happiness has so much power,
It brings joy to everyone,
What peace of mind happiness can show,
Forget the troubles of the past.
Never fear that it will go for it could always grow
and tomorrow there it will be,
For happiness can set you free!
The theme refelcts on the perspective by licking a whole inthe system.