premise: Exactly six petri dishes—labeled dish 1 through dish 6—are to be stored in an otherwise empty refrigerator. There are three available shelves—the bottom shelf, the middle shelf, and the top shelf. The placement of the dishes must be consistent with the following conditions: No more than three dishes are stored on any shelf. Dish 2 is stored at least one shelf above dish 6. Dish 6 is stored either one shelf above or one shelf below dish 5. Dish 1 is not stored on the same shelf as dish 4. If dish 5 is the only dish stored on the bottom shelf and if exactly two of the dishes are stored on the middle shelf, then which one of the following is a pair of dishes that must be among the dishes stored on the top shelf?
hypothesis: dish 2 and dish 3