Validity of alternative 9/11 theories.

• Position: Terrorism

One in two Americans has doubts about the government's account of 9/11 and, after viewing video footage of World Trade Center Building Ts collapse, 46% suspect that it was caused by a controlled demolition, reveals a national survey by the polling firm YouGov. Building 7, a 47-story skyscraper, collapsed into its own footprint late in the afternoon on 9/11.

Among the poll's findings:

* 38% of Americans have some doubts about the official account of Sept. 11,2001; 10% do not believe it at all; and 12% are unsure about it.

* 46% are not aware that a third tower collapsed on 9/11. Of those who are aware of Building Ts demise, only 19% know the building's name.

* 41% support a new investigation of Building 7's collapse, compared to 21% who oppose it.

"The poll shows quite clearly what we already knew. Most people who see Building 7's collapse have trouble believing that fires brought it down," says Richard Gage, a member of The American Institute of Architects and founder of Architects & Engineers for 9/11 Truth, which supports the ReThink911 campaign that sponsored the poll.

"It simply doesn't look like a natural building collapse, and that's because all the columns have been removed at once to allow it to come down symmetrically in...