Apopulation of mosquitoes is exposed to the pesticide ddt for several generations. at the end of that time, most individuals in the population are resistant to ddt. the most likely reason is

The reason is the development of KDR genes and GSTe2 genes through mutation.

Explanation:

The development of these genes result in metabolic and target resistances.

Note that, the metabolic resistance changes in a mosquito systems brings about more rapid detoxication of the insecticide than normal,preventing it from reaching the target site.

The target site resistance also happen by mutation. This prevent the insecticide from binding to the intended target site of the receptor, making the insect unaffected.

b is the best answer for this question.