Why Might the Yersinia Pestis from a Patient with Pneumonic

Why might the Yersinia pestis from a patient with pneumonic plague be more dangerous than the same organism from fleas?

A) The organism mutates in a person with pneumonic plague, so is more dangerous.
B) The organism involved in pneumonic plague is resistant to multiple antibiotics.
C) The organism acquired this way is already fully virulent, so is especially dangerous.
D) Y. pestis in the lungs has a polysaccharide capsule while that in fleas does not.
E) These are all true.