I'm experimenting with the STACK multiple choice question type (radio in this case). I've been successful with a few questions so far, but I'm getting an error when I try to include plots. I can successfully use the display option when it is text, but not when it is a plot. To troubleshoot I've used the brief example at https://stack2.maths.ed.ac.uk/demo/question/type/stack/doc/doc.php/Authoring/MCQ.md.
I've attached two screen captures. The first contains my question variables and text (I've made sure the plots work). My model answer is ta and my prt is comparing ans1 with 1 (this works if the display for each answer is text instead of a plot). The second contains the last of the three plots and then the error I am getting.
Any suggestions are greatly appreciated.
