which of the flights from pittsburgh to baltimore on july twenty fifth 1991 carries the smallest number of passengers 
return the  flights ;return #1 on july twenty fifth 1991 ;return #2 from pittsburgh ;return #3 to  baltimore ;return the  number of  passengers for each of #4 ;return #4 where #5 is  the  smallest
['select', 'filter', 'filter', 'filter', 'group', 'comparative']