They are on shelf B in aisle 1.
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On both sides of aisle 1, how many shelves are there at a department store? Are there two shelves on both sides of each aisle. Do we have to use 'in' before 'aisle'? What about using 'in' before 'shelf B'? Do we have to use 'on' before 'shelf B'?
It depends on what kind of store and what department to determine the number of shelves. In a women's clothing department of a store, you might find 3 or 4 shelves, depending on the articles of clothing on display. In children's departments, perhaps more.
Yes, "on" is to be used with "shelf" and "in" with "aisle."