DDT was used to eradicate mosquitoes, which are malaria vectors. At first, the eradication was successful, but DDT became less effective in controlling the mosquito over time. What is the reason behind this outcome?

• A. New species have emerged.
• B. DDT's chemical composition had changed.
• C. Mosquitoes with DDT-resistant alleles survived and reproduced.
• D. The environment had become more polluted than before.

Answer: (C)