Sentence:  After paying tribute to the conductor and his white-clad youthful students , President Kennedy said , `` As an American I have the greatest possible pride in the work that is being done in dozens of schools stretching across the United States - schools where devoted teachers are studying with interested young men and women and <WSD>opening</WSD> up the whole wide horizon of serious music '' . 
Meaning of the word marked with <WSD> tags:  open up an area or prepare a way