PLEASE HELP 20 POINTS Which of the following statements explains how strains of methicillin-resistant Staphylococcus aureus appeared two years after doctors began using the antibiotic methicillin?

The drug-resistant bacteria existed in the population but did not have an advantage until the environment changed with the introduction of methicillin.
In response to the treatment with methicillin, the bacterial population gradually began to synthesize cell walls using a protein that was not affected by the drug.
The bacteria that survived the drug methicillin, developed an immunity to the drug.
The bacteria mutated in response to the drug and began making drug-resistant versions of proteins need to build cell walls.