Mosquitoes in tropical regions can carry and transmit the malaria parasite to humans. the mosquitoes used to be killed in these regions by spraying them 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 presence of ddt. how can you explain this phenomenon?
a) all of the mosquitoes must've undergone a mutation for ddt resistant offspring, which evolved into a ddt resistant population
b) some of the mosquitoes must've undergone for ddt resistance and produced similar kind of restraint offspring, which would've been selected by nature
c) all of the mosquitoes must've slowly increased their tolerance level to ddt and ultimately would have become completely resistant to ddt