Final answer:
The category A agents of bioterrorism are not limited to one type of organism; they include bacteria, viruses, fungi, and parasites, classified based on their potential for high impact in bioterrorist events.
Step-by-step explanation:
The true statement concerning the category A agents of bioterrorism is that they can comprise bacteria, viruses, toxins, fungi, and parasites. Category A agents are classified based on their high potential for mass dissemination, high mortality rates, and potential for major public health impact, which necessitates special action for public health preparedness.
For instance, anthrax, caused by the bacterium Bacillus anthracis, is a Category A agent that is bacterial in nature. Smallpox, caused by the variola virus, is a viral member of Category A agents. Thus, the classification into Category A does not depend on the type of organism, but rather on the severity of the disease they can cause and their potential use in bioterrorism attacks.