hello all...
As everyone on earth, I watched those videos with shock and horror...
Concerning the fact that the towers withstood those incredible collisions, it is true that they were designed to resist the impact of an 707. And they did this beautifully : they barely moved upon impact !!!
The reason they collapsed, though is because they were designed to resist "domestic" fires, a.k.a a fire that burns at about 800 °C... The kerosene fire that was the case here burned at more than 2000°C !!! it MELTED the supports !
no doubt those guys chose these airplanes carefully ...
Regards to all you americans out there !! we sympathize.