Anew and effective antibiotic becomes widely used for a particular species of bacteria. after some time, an antibiotic-resistant strain of the bacteria becomes prevalent. which mechanism explains this phenomenon?
the bacteria undergoes genetic drift, leading to formation of a new gene pool and thus evolving a new characteristic.
although less common previously, the resistant strain becomes more prevalent due to natural selection.
the bacteria undergoes genetic flow, thus creating a new gene pool and evolving into a new species.

Use of Antibiotic is the main reason for development of antibiotic-resistant bacteria.
When a person is given the dose antibiotics, sensitive bacteria are killed, but resistant germs are sometimes left to grow and and increase in number.

Antibiotic resistance is the ability of an organism to stay unaffected by  the effects of antibiotics. Natural selection caused by random mutation is the main cause of Antibiotic resistance.

Hence,The right answer is : Option B: "Although less common previously, the resistant strain becomes more prevalent due to natural selection."

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