1. the 9/11 attacks were not an inside job, however, the USA government knew in advance that it was going to take place. They didnt do anything (most likely to justify the eastern conflicts) and let it happen.
2. smoke from fires isnt always black, it is very often white or grey due to the chemicals in the fire.This can be due to the different materials inside the building rather than the building itself, such as plastics, water vapor, wood and tile.
3. the structural integrity of the towers were already questioned and im pretty sure it was explained somewhere that the towers stability was already faulty, causing the "pancake" effect we saw.
all in all, the towers fell because terrorists attacked it, the government let it happen.
thats it, thats the story.