Final answer:
The claim that many September 11th hijackers used student visas to enter and reside in the U.S. before the attacks is true, evidencing the weaknesses in the U.S. immigration system exploited by Al-Qaeda terrorists.
Step-by-step explanation:
The statement that many of the September 11th hijackers used student visas and had lived in the United States for some time before the attacks is true. These terrorists indeed exploited the U.S. immigration system to enter and reside in the country while they prepared for their operations. The 9/11 attacks, carried out by members of Al-Qaeda, dramatically demonstrated the vulnerabilities of the U.S. immigration policies, leading to significant changes in how visas are processed and monitored in the aftermath. Some hijackers attended flight schools in the U.S., aiding them in their ability to pilot the hijacked planes that crashed into the World Trade Center, the Pentagon, and, due to the action of passengers, a field in Pennsylvania instead of its intended target in Washington, D.C.