It's the terror attack that changed the course of America and the world. This weekend marks the 20th anniversary of 9/11. Almost 3000 people from 78 countries were killed on September the 11th, including the four hijackers aboard the planes. It sparked the war in Afghanistan - America's longest-running war. Worldwatch's Perlina Lau spoke to a survivor who was in the tower when the first plane hit.