GRE阅读高频机经原文及答案：胡蜂吃天牛

　　37. 胡蜂吃天牛

　　Stem borers are insect pests that often ruin North American corn crops. On some other continents, crop damage by stem borers is controlled by a certain species of wasp. Since these wasps eat nothing but stem borers, importing them into North America will keep crop damage from stem borers under control without endangering other North American insect species.

　　Which of the following is an assumption on which the argument depends?

　　Corn is the principal food of stem borers that live on continents other than North America.

　　The wasps are capable of surviving in North America long enough to eat significant numbers of stem borers.

　　No wasp in North America is closely related to the species of wasp that eats stem borers.

　　On continent other than North America, the wasps control stem borers more effectively than does any other pest control

　　measure.

　　Corn crops on continents other than North America are not damaged by any insect pests other than stem borers.

　　答案：B