Well, it finally happened: Despite having two chances on a multiple-choice question, I spoiled my perfect score in the massive open online course I'm taking from the University of Texas.
However, I'm going to invoke the age-old excuse of many a student and argue that there was something wrong with the question in "Take Your Medicine -- The Impact of Drug Development." The question had to do with whether it is safe for a patient to split a tablet in half. Course rules prohibit me from discussing the fine print here. I'll just argue that, although one answer might be better than the others, I don't think it's flat-out correct.
On a brighter note, I've not yet needed two chances to get a true-false question correct.