Which of the following blood culture results would be classified as persistently positive, according to the modified Duke criteria?
a. A typical IE microorganism identified from 2 different blood cultures from the same site.
b. A typical IE microorganism identified from 2 different blood cultures from 2 separate sites, drawn 15 minutes apart.
c. Two positive blood cultures drawn 6 hours apart.
d. At least 2 positive cultures of blood samples drawn 12 hours apart