Final answer:
The 9/11 hijackers were responsible for committing acts of sabotage leading to the death of thousands, which aligns with the subject of the question. Timothy McVeigh's act of terrorism in Oklahoma City was another significant but separate event. Sit-ins were the protest tactic that fueled both the Velvet Revolution and the Arab Spring.
Step-by-step explanation:
The student's question asks which individual or group was responsible for committing acts of sabotage that may have caused the death of hundreds of innocent people. Based on the information provided, the individuals notorious for such acts include The Unabomber, Ted Kaczynski, who engaged in a nationwide bombing campaign; the 9/11 hijackers who committed the deadliest terrorist attack on American soil; Timothy McVeigh, who orchestrated the Oklahoma City bombing; and the Tsarnaev brothers, who were behind the Boston Marathon bombing.
For the specific question being addressed, the 9/11 hijackers were responsible for an act of sabotage that resulted in the death of nearly 3,000 innocent people when they hijacked airplanes and crashed them into the World Trade Center and the Pentagon. Another mentionable individual is Timothy McVeigh, who was motivated by a desire to start a revolution against the government's control and committed what was at the time the worst act of terrorism on American soil by blowing up the Alfred P. Murrah Federal Building.
The protest tactic that ignited both the Velvet Revolution and the Arab Spring was not terrorist bombing but rather sit-ins, involving nonviolent demonstration and occupation of public spaces.