You've Just Isolated a New Bacterium in Pure Culture, and You

You've just isolated a new bacterium in pure culture, and you culture it on a general purpose medium where its cells have a coccobacillus morphology.When you examine the cells after culturing on a variety of differential media, you find that in some cases, the cells appear as coccobacillus, but in others, they can be filamentous, cocci, or club-shaped.The best explanation for this observation is that

A) the media were incubated at an incorrect temperature.
B) the differential media are contaminated.
C) the microscope is out of adjustment.
D) the bacterium is pleomorphic.
E) your culture has become contaminated.