Piagets famous ? problem demonstrates preoperational childrens difficulty with?

Question

THREE MOUNTAIN; DUAL REPRESENTATION
THREE MOUNTIAN; HIERARCHICAL CLASSIFICATION
CLASS INCLUSION; HIERARCHICAL CLASSIFICATION
CLASS INCLUSION; DUAL REPRESENTATION

THANK YOU FOR THE HELP IAM SO STUCK

Answer 1

http://psychology.about.com/od/piagetstheory/p/preoperational.htm

Also -- please learn to spell L A N G U A G E.