What is this? And when answer please have an explanation for it

Nextend of semester testsubmit testreader toolsinto-samosquitoes in tropical regions can carry and transmit the malaria parasite to humans. the mosquitoes used to be killed in these regions by sprayingthem with the insecticide ddt. the mosquitoes that were earlier sensitive to ddt are now not killed by ddt and grow and multiply even in the presenceof ddt. how can you explain this phenomenon? oa.all of the mosquitoes must have undergone a mutation for ddt resistance and produced similar kind of resistant offspring, whichevolved into a ddt resistant population.b.some of the mosquitoes must have undergone a mutation for ddt resistance and produced similar kind of resistant offspring, whichwould have been selected by nature,oc.all of the mosquitoes must have slowly increased their tolerance level to ddt and ultimately would have become completely resistantto ddtresetnextnext