E. coli is a species of bacteria that causes many different infections in humans. Certain E. coli strains have developed resistance to antibiotics, making infections with these strains difficult to treat. How do bacteria such as E. coli, which reproduce asexually, gain new traits such as antibiotic resistance?

A.
by mutating their DNA in response to environmental conditions to gain beneficial traits
B.
by adapting to changes in environmental conditions without undergoing changes in their DNA
C.
by producing offspring with new gene assortments from genetic recombination, which increases diversity in a population
D.
by undergoing spontaneous mutations when they replicate, which increases genetic variation in a population