The fruit fly drosophila melanogaster has an allele that confers resistance to ddt and similar insecticides, laboratory strains of d. melanogaster have been established from flies collected in the wild in the 1930s (before the widespread use of insecticides) and the 1960s (after 20 years of ddt use) lab strains established in the 1930s have no alleles for ddt resistance. in lab strains established in the 1960s, the frequency of the ddt-resistance allele is 37%. which statement is correct?
a) resistance to ddt evolved in some fruit flies in order to allow them to survive
b) alloles for ddt resistance arose by mutation during the period of ddt use because of selection for pesticide resistance
c) the evolutionary fitness associated with the heritable trait of ddt resistance changed once ddt use became widespread