Intelligence is a 1.___ that is difficult to2. ___ ,and it can mean different things to 3.___ people.The difficulty in defining what intelligence is has created 4.___ among those studying it.Today the definition of intelligence 5.___to be characterized by 6.___ is studying it at 7.___ moment.The 8.___ of intelligence can be 9.___ as far 10.___as the 1800's.