In which year was there the highest real gross domestic product, 2017, 2016, or 2015?
return real gross domestic product ;return #1 In 2017 ;return #1 In 2016 ;return #1 In 2015 ;return which is highest of #2 ,  #3 ,   #4
['select', 'filter', 'filter', 'filter', 'comparison']