The most likely reason for the development of resistance against pesticides in insects damaging a crop is:
The most likely reason for the development of resistance against pesticides in insects damaging a crop is:
random mutations
genetic recombination
directed mutations
acquired heritable changes.
Solution
The most likely reason for the development of resistance against pesticides in insect damaging a crop is random mutations, because environmental stress, i.e. pesticides does not cause direct changes in genome $\mathrm{m}$ instead, it simply selects rather persisting mutations which result in phenotypes that are better adapted to the new environment in certain pesticides.