In which year was the price of wheat the lowest: 1877, 1878, or 1886?
return wheat ;return prices of #1 ;return #2 In 1877 ;return #2 In 1878 ;return #2 In 1886 ;return which is lowest of #3 ,  #4 ,   #5
['select', 'project', 'filter', 'filter', 'filter', 'comparison']