The causative agent of Lyme disease is ________, which is carried primarily by the ________. A) a flavivirus / Ixodes sp. (deer tick) B) Yersinia pestis / Xenopsylla cheopis (rat flea) C) Rickettsia prowazekii / Culex species (mosquito) D) Borrelia burgdorferi / Ixodes sp. (deer tick)