The first thing I point out to people who ask me about it is the "resistance paradox." The WTC towers' top portions fell through the steel and concrete of the lower portions about as fast as chunks and pieces from them were falling through the adjacent air. Assuming a collapse, this would indicate the lower portions provided little more resistance to the tops than air would. Yet the top portions disintegrated while falling,This is an irresolvable paradox, material cannot simultaneously present high and low resistance. Controlled demolition on the other hand explain both phenomena. There are many aspects of the 9/11 WTC events which to me indicate controlled demolitions.