A question i was marked down for as incorrect. Which of the following can create a flammable dust oil soaked rags, Cleaning fluids, cardboard, grain. I answered Cardboard and was marked as incorrect with a quote "Cardboard is unlikely to create dust" having worked with cardboard packaging for many many years the quote is incorrect and misleading. I now get why grain is the answer but cardboard also creates a flammable dust from experience and feel the answer is ambiguous so another example should be used...it definitely creates a dust that would be flammable..other than that a good course...