Many pathogenic bacteria species are becoming resistant to antibiotics. explain how such adaptions can develop through the process of natural selection ?

The genes to be resistant to an antibiotic already exist in the bacteria's genes.  Those whose phenotypes are resistant to the antibiotic will survive the antibiotic which kills the other non-antibiotic-resistant bacteria.  The surviving bacteria will then asexually reproduce, producing more antibiotic-resistant bacteria.

Where are the phrases