That proves my point - when there is only one representative of each sort (be it from a collection of two or two thousand) it is reasonable to ask which one.

If you had shown me seven glasses made up of four pints of Thwaites Best Bitter, and three of Greene King's Abbot Ale Everard's Beacon Ale, and asked me, "here are 7 pints of ale, which one would you like to try first," I would still think you were asking which glass, not which ale. (And I would select the furthest away, on the grounds that by the time I got to the seventh, I would need it to be near at hand!)