Simplify the following text for a Grade 12 native English-speaking person.
Original: Ives had composed two symphonies , but it is with The Unanswered Question ( 1906 ) , written for the highly unusual combination of trumpet , four flutes , and string orchestra , that he established the mature sonic world that became his signature style .
Simplified: Perhaps the piece which is most often heard today is the short fanfare The Unanswered Question ( 1908 ) , written for the very unusual combination of trumpet , four flutes , and string orchestra .