Since the Cardiovascular and Lymphatic Systems Are Not Directly Accessible

Since the cardiovascular and lymphatic systems are not directly accessible to microbes ________.

A) it was initially believed that the systems lacked normal biota,however the Human Microbiome Project suggests that low levels of microbes may exist in the healthy state
B) both systems are sterile in the healthy state
C) the abundant microbiota enter via the gastrointestinal tract then cross the blood vessels
D) the Human Microbiome Project confirmed that only pathogens exist in both systems