How is antibiotic resistance an adaptation?

A.
The trait giving bacteria antibiotic resistance has reproductively isolated groups of bacteria.
B.
Antibiotic resistance has caused antibiotics to become more specialized, thus adapting the antibiotics to particular bacteria species.
C.
Antibiotic resistance makes it more difficult for bacteria to infect hosts, thus is a selective advantage for the host.
D.
The trait giving bacteria antibiotic resistance has become common, giving bacteria with the trait a selective advantage.

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