Answer:
Al-Queda was responsible. Ramzi Yousef was a very important tool in the planning and execution of the 9/11 attacks.
2 planes were involved, and they attacked the Twin Towers in New York.
They most likely attacked the United States because it would show their gall, and it was an enemy to Al-Queda.
The results were the Twin Towers collapsing in on themselves, thousands of carcinogens being released, and around 3,000 people dying just that one day. Due to the carcinogens that civilians and firefighters, EMTs, and First responders experienced, a lot of them ended up dying from cancer. Not to mention numerous political advancements