Which of the following is an example of directional selection?

Directional selection is a type of natural selection where individuals with a phenotype at one extreme of a range of variation are favoured over other individuals with phenotypes closer to the mean or at the opposite extreme. This results in a shift in the frequency distribution towards the favoured phenotype over time.

The example is given, a population of bacteria becoming resistant to antibiotics, is an example of directional selection. When antibiotics are introduced, the bacteria with mutations that confer resistance to the antibiotic are favoured over those without the mutation, and as a result, the frequency of the resistant bacteria increases over time.