I suggest you turn off Ace by unchecking the "Use ace" checkbox. Ace makes it harder for you to update the student answer and you'd have to change the Ace language when the drop-down list changes. If you really want to do things like that, please look at the CodeRunner source code, particularly amd/src/aceinterface.js, and the Ace API documentation.
I'll consider implementing the drop down menu, with Ace editor language selection, in my next development binge, at the end of this year. I don't wish to spend time on workarounds in the meantime; they're likely to take more effort than doing the job properly!