You may notice once in a while that you can't see the graph that you're supposed to see in one of your questions in your quiz. This happens only in Chrome and Safari and is very easy to fix. Just follow the steps below.
Minimize and maximize your browser
Notice in the example below that the graph for this question seems to be invisible.
Call technical support if this doesn't solve your problem
Please see the help article Where else can I go to get help? for information on how to contact technical support.