The correct option is C Yersinia pestis
Plague is a deadly infectious disease that is caused by the enterobacteria, Yersinia pestis. 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. The bacteria multiply inside the flea, sticking together to form a plug that blocks its stomach and causes it to starve. The flea then bites a host and continues to feed, even though it cannot quell its hunger, and consequently the flea vomits blood tainted with the bacteria back into the bite wound.