Answer:
The world trade center (Twin towers) and the Pentagon
Step-by-step explanation:
Since these two (or should I say three) buildings were important to the U.S because they had Trading for the U.S and the Pentagon was more like a security base. After that they were going to hit the White house, but the heroic passengers of the hijacked airplane attacked the hijackers so they wouldn't hit the white house and kill Obama. (R.I.P. heroic people)