I find the math test answer hilarious.
Of course a single piece of cake won't cause diabetes but there is an increasing body of evidence that sugar does cause diabetes on a population level at least and the mechanism behind it seems to be fructose that is culprit on the individual level. So I can't see a problem with Sugar causes diabetes. Not that I ever had much sugar so you can catch it anyway, it doesn't have to be due to a high sugar consumption.