Facts and history tend to be the biggest give away concerning 911. I'll give you a small set of facts which tend to answer many questions.
1. Before 911 two American oil companies which I will not name have been trying to build a gas pipeline across Afghanistan from the Caspian sea. The Taliban refused to allow such a venture.
2. After 911 the Taliban have been removed from power and the trans Afghanistan pipeline is currently under construction.
3. Before 911 there was no oil being pumped from Iraq to the western world.
4. After 911 there is oil being pumped from iraq to the western world.
You can either believe that the invaders of those two afore mentioned Countries planned to take those resources before they invaded or you can believe that they just happened to stumble on such plans while they were sat around bored in those Countries.
History speaks for itself.
Mod Note: This post was spliced from "The Great 9/11 Challenge" as it didn't meet the requirements of that thread