Youyou's mother used some kind of insecticide to kill mosquitoes for a long time. It was fine at first, but it got worse later. What is the most likely reason for this phenomenon? (explain why)
The answer is C, because of the long-term use of pesticides to kill mosquitoes, all the mosquitoes with poor drug resistance have been killed, and the rest are mostly genetically resistant mosquitoes, which are breeding. Over time, only drug-resistant mosquitoes remain, and the effect of drugs is getting worse and worse. You can also understand it as the survival of the fittest among mosquitoes.