Lihat Juga

• The social problem : a reconstructive analisys
  oleh: Ellwood, Charles A
  Terbitan: (1924)
• The problem of cultural differences
  oleh: Park, Robert E.
  Terbitan: (1931)
• Some Problems of the new stone age
  oleh: Peake, Harold J.E
  Terbitan: (1937)
• Acres and people : the eternal problem of China and India
  oleh: Wilcox, E.V
  Terbitan: (1947)
• The problem of Krakatau as seen by a botanisct
  oleh: Backer, C.A
  Terbitan: (1929)