I've just got to the Visualizing Your Data Knowledge Check & can't see , or respond to questions 2, 4 or 5.  Instead of the questions, I just get a single line of error text reading, "An error occurred. Unable to load drag and drop problem."  I've tried clearing my browsing data & signing back in after restarting my laptop, but the error persists.  
Can anyone advise me how to resolve this, please?