TOEFL Reading: ETS-TOEFL阅读机经 - 92ZBK13G537F6868L$

In paragraph 5, the author mentions the Chinese use of predatory ants to control pests in order to A. support the claim that using pests' natural enemies is a pest control technique that has been known for a long time B. show that pests' enemies introduced unintentionally have proved more dangerous than those introduced intentionally C. help explain that when pests' enemies find enough resources, they can become pests themselves D. argue that a pest insect in its native habitat always has a predator in that habitat