What are the names of schools with the top 3 largest size?
return schools ;return size of #1 ;return #1 where #2 is highest ;return #1 besides  #3 ;return #4 where #2 is highest ;return #4 besides  #5 ;return #5 where #2 is highest ;return #3 ,  #5 ,   #7
['select', 'project', 'superlative', 'discard', 'superlative', 'discard', 'superlative', 'union']