Answer choice D, as it shows that the experiment is repeated.
Answer: <span>Normal microbiota directly kill invading organisms.
Some bacteria that reside in our body are useful to combat pathogenic microorganisms. Those bacteria, like lactobacillus and E.coli, inhibit the growth of those pathogenic organisms by taking, for example, oxygen and nutrients from them, or even changing the local ph. They can also produce metabolites that make the environment impossible to live for the intruders.
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The answer is B) Limiting factors.
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