Final answer:
Prion (c) is a protein substance with no DNA or RNA that is thought to be the cause of mad cow disease.
Step-by-step explanation:
The protein substance with no DNA or RNA that is thought to be the cause of mad cow disease is prion (c). Prions are infectious particles that consist of protein and replicate by changing the shape of normal proteins into an abnormal form. They are associated with several progressive brain disorders, including mad cow disease and Creutzfeldt-Jakob disease.