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Malaria is a tropical disease caused by a single-celled parasite. People become infected with malaria when they are bitten by a mosquito carrying the parasite. Infection with the malaria parasite causes health problems, and each year over 200 million people are infected and 1 million die from malaria. To prevent malaria, humans have tried killing the mosquitoes that spread the parasite. In the 1940's, the insecticide DDT was used as it was found to be highly effective at killing mosquitoes. Spraying with DDT killed 99% of mosquitoes and significantly reduced the number of people getting malaria.Soon after the use of DDT, health workers in Africa discovered that mosquito populations had evolved resistance to the insecticide. Each subsequent year of DDT application resulted in fewer exposed mosquitoes dying. By the end of the 1940's DDT was no longer effective in some regions and was replaced with other insecticides. Eventually, mosquitoes evolved resistance to each insecticide used to combat malaria, causing a serious health problem.Which of the following is the best explanation of the process that caused mosquito populations in Africa to become resistant to DDT?a. The mosquitoes evolved resistance to malaria in order to survive.b. Some mosquitoes were naturally resistant to DDT due to variation in the genome of mosquitoes. Since those mosquitoes survived the DDT, they were able to pass on their resistance to their offspring.c. The immune systems of mosquitoes exposed to DDT developed resistance, which was passed onto their offspring. Each generation of mosquitoes had more and more antibodies against DDT.d. DDT caused a much higher rate of mutations in the DNA of mosquitoes. This higher rate of mutation meant that there were more mutants in the DDT resistance gene.

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