Final answer:
Danielle remembered the September 11 attacks, in which al-Qaeda terrorists hijacked planes and crashed two of them into the Twin Towers in NYC, resulting in nearly 3,000 deaths.
Step-by-step explanation:
Danielle is referring to the September 11 attacks, which occurred on the morning of September 11, 2001. During this tragic event, members of the Islamist terrorist group al-Qaeda hijacked four commercial airliners. Two of these planes were flown into the Twin Towers of the World Trade Center in New York City, causing both towers to eventually collapse. The attacks resulted in the deaths of nearly 3,000 people, including 343 New York City firefighters. This was part of a coordinated attack that also targeted the Pentagon in Washington, D.C. and, due to heroic passenger intervention, led to a crash in a field in Pennsylvania instead of its likely intended target in Washington, D.C.