The microorganisms present on day 5 were
(1) newly added from the sterile culture medium
(2) offspring of antibiotic-resistant individuals
(3) organisms that were all present on day 1
(4) offspring with no resistance to the antibiotic
The microorganisms present on day 5 were "(4) offspring with no resistance to the antibiotic" since antibiotics would have eliminated an unfit contenders.
