The Term Complex as Used in "M.tuberculosis Complex

The term complex as used in "M.tuberculosis complex"

A) means that the identification of the organism is complex and is only done in very large reference laboratories.
B) is used to describe two or more species whose distinction is complicated and of little or no medical importance.
C) refers to a set of organisms that are genetically indistinguishable but that are phenotypically different.
D) All of the above are correct.