Final answer:
The correct answer is option D.Unexplained casualties.
Step-by-step explanation:
The question pertains to the indicators of a radiological attack, which involves the intentional release of radioactive materials to cause harm. Among the options provided, unexplained casualties would be a likely indicator of a radiological attack. A radiological attack would not necessarily manifest as glowing material or accelerant odors, and a mushroom cloud would be more indicative of a nuclear explosion rather than a radiological 'dirty bomb' attack.
Radiological materials may emit radiation that is not detectable by human senses such as sight, smell, or taste. The impact of radiation exposure can range from acute radiation sickness to long-term health effects like cancer, often with casualties that may be unexplained without appropriate detection equipment. In this respect, the presence of unexplained medical issues among a population could suggest exposure to a radiological agent.