Make the debug statement make more sense.
I suppose you can append '&debug' to an exercise url if there is already a ? to set off variables in the URL, otherwise, you need to append ?debug to 'addition_1.html', 'addition_1.html?debug' works while 'addition_1&debug' does not. This is probably obvious to most users, but still seems like it could be better described.
&debug should be ?debug
oh yeah, underscores screw up formatting
In production already.
Updated Good Examples (markdown)