After September 11th

Gap-fill exercise

Use the definite article only when needed AND put in xxx where no article is needed!
All over the world people were shocked when they heard news and saw pictures of attack on World Trade Center. Many of people who had worked in Twin Towers lost their lives and many had to stay in hospital for weeks. We know that history is full of tragedies, but September 11th was one of worst tragedies in history of United States.