Microorganisms in the Human Colon Are More Often Being Described

Microorganisms in the human colon are more often being described as mutualistic with human hosts rather than commensalistic.Why has this change in the definition of a symbiotic relationship occurred?

A) As we learn more about the ecology of the human microbiome,we recognize our dependence on these organisms for immunity,vitamin production,and other essential processes.
B) As we learn more about the ecology of the human microbiome,we have learned that these organisms are dependent on the nutrients that we provide for their survival.
C) As we learn more about the makeup of the human digestive tract,we realize that some microorganisms are potentially pathogenic while others are not.
D) All of the choices are correct.