What event marked the first occasion of chemical, biological, and radiological terrorism in U.S. history?

The post 9/11 anthrax attacks represent the first occasion of chemical, biological, and radiological terrorism in U.S. history due to the deliberate use of anthrax spores, a biological agent, in a series of mailings that occurred in the weeks following the September 11 attacks. This event involved letters laced with anthrax being sent to various news agencies and government officials, resulting in widespread fear, public health responses, and discussions on bioterrorism preparedness and response measures.

These attacks highlighted vulnerabilities in national security related to biological threats and underscored the need for enhanced surveillance, rapid response capabilities, and strategies to deal with potential biological agents. The anthrax cases were also significant in shaping future policies regarding biological threats and the handling of such crises by public health and law enforcement agencies.

In contrast, the other events listed in the choices do not fit the criteria of involving chemical, biological, or radiological terrorism. Each of those incidents centered around different forms of attacks, such as explosives or conventional weaponry, rather than the deliberate release of biological agents.