WTC Buildings Destroyed - New York, 9-11-2001

What do you think (or believe) caused the physical destruction and collapse of the World Trade Centers in New York City on September 11th, 2001?
- faulty, poor grade construction steel
- jet airliners crashing into the towers
- subsequent fires weakening the structures
- a combination of airliners crashing & the fires
- a bomb or missile attached to the plane(s)
- combination of all of the above
- angry UFO alien death beam ray
- strategically placed demolition charges
References:
http://69.28.73.17/911bottomline.html
http://www.davesweb.cnchost.com/nwsltr67.html