求教一个语法问题

酸奶派派

“More selective than most chemical pesticides in that theyordinarily destroy only unwanted species, biocontrol agents (such as insects,fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests.” 求指教此句子中的“they”是指 “mostchemical pesticides” 还是 “biocontrolagents ”？欢迎讨论

老白在费城

biocontrol agents
因为句意说的是BA比most chemical pesticides更selective因为they ordinarily destroy blah blah