Columbia subject headings:
Heroes--United States.
Hijacking of aircraft--United States.
Memorials--Washington (D.C.)
September 11 Terrorist Attacks, 2001.
United Airlines Flight 93 Hijacking Incident, 2001.
Harvard subject headings:
Heroes--United States
Hijacking of aircraft--United States
Memorials--Washington (D.C.)
September 11 Terrorist Attacks, 2001.
United Airlines Flight 93 Hijacking Incident, 2001.
Princeton subject headings:
Heroes--United States.
Hijacking of aircraft--United States.
Memorials--Washington (D.C.)
September 11 Terrorist Attacks, 2001.
United Airlines Flight 93 Hijacking Incident, 2001.