Why should laboratory professionals look for contamination of a specimen by normal microbial flora?

A) Contaminated specimens will have much amorphous debris that also goes with them.
B) Normal flora always preclude the possibility of a pathogen infecting the area where they reside.
C) The normal flora will be found in clumps, and any pathogenic bacteria will be found with the normal flora.
D) Contamination of specimens with normal flora that are not collected from sterile sites diminishes the value of the culture studies.