The correct option is C Xenopsylla
Contrary to popular belief, rats did not directly start the spread of the bubonic plague. It is mainly a disease in the fleas (Xenopsylla cheopis) that infested the rats, making the rats themselves the first victims of the plague. Infection in a human occurs when a person is bitten by a flea, that has been infected by biting a rodent that itself has been infected by the bite of a flea carrying the disease.