Building 7 was a 47-story skyscraper and was part of the World Trade Center complex. It collapsed at 5:20 pm on September 11, 2001 in 6.5 seconds. It was not hit by an airplane. Most people have yet to learn about Building 7.
I invite you to go to http://www.BuildingWhat.org and learn about Building 7 and about this TV ad campaign. You will find a video showing the collapse of this skyscraper and ways to contribute to the campaign.