Context: It was awful to think that there had been 4 planes hijacked that day , and how it could get much , much worse . Later that night when I got home , I was glued to the TV .... watching in horror as the Twin Towers came down and all the rescue workers and other people who were trapped in the buildings as they fell . It all seemed so surreal . So , so sad . At that time they thought there may have been 50,000 people in the building , and so many people were missing .
Question: What is this event known as ?
Option 0: It is known as Y2 K
Option 1: It is known as Black Monday
Option 2: It is known as 9/11 .
Option 3: It is known as D - Day
Answer: 2