Okay, I'm also stuck on this cupboard problem. Thought maybe it was a matter of counting which things are earthy, which watery, etc. Does this require some background in chemistry to recognize what each shelf's components would do or something?
its the order in which the things are placed on the shelves in the cabinet: aqua regia is in position two on the top shelf (water), triple A battery is third on the second shelf (electricity), kerosene is in the third position on the third shelf (fire), and soil samples are on the bottom shelf in the fourth position (earth/leaf)