"You should sleep."
Translation:Du solltest schlafen.
I considered if this was meant to be subjunctive "du solltest schlafen" you should sleep (but you might not) when I saw the correct solution 1. However if this were the reasoning, the answer "Sie sollen schlafen" wouldn't be available as a correct solution 2, meaning you are supposed to sleep. I'm not entirely committed to this but I did find supporting evidence.
Here are citations I used: http://www.verbix.com/webverbix/German/sollen.html
Additionally I submitted "du sollst schlafen" as an answer along with this comment, but I think this may be useful for a comment if anyone else is trying to figure out sollen.