The correct answer is option 3: virus.
Polio is a highly contagious viral disease that is caused by the poliovirus. The poliovirus is part of the family of viruses called enteroviruses, which primarily infect the gastrointestinal tract.
Option 1: Bacteria is not the cause of polio. Bacteria are single-celled microorganisms that are larger and structurally different from viruses.
Option 2: Fungi are also not the cause of polio. Fungi are a separate kingdom of organisms, including yeasts and molds, that are different from viruses.
Option 4: Worms do not cause polio. Worms are multicellular organisms that belong to the animal kingdom and are not responsible for viral infections.
In conclusion, polio is caused by a virus, specifically the poliovirus. It is important to note that effective vaccines have been developed to prevent polio, and efforts to eradicate the disease are ongoing worldwide.