NEW YORK - As America marks the anniversary of the worst terror attack on U.S. soil, many remembered the countless lives lost and selfless acts by the brave responders on September 11, 2001 — both human and four-legged.Nearly 3,000 people were killed when terrorist-piloted planes slammed into the World Trade Center, the Pentagon and a field in Pennsylvania.Thousands of firefighters and emergency medical personnel responded to Ground Zero, including more than 300 specialized canine search and rescue (SAR) teams in the days following.