A、1780’s. B、1770’s. C、1870’s. D、1880’s. C信息题。录音中提到The wave model，formulated by Johannes Schmidt in the 870’s…因此选项C是答案。

J: Divergence is by no means the only possible tendency. Some scholars introduced a "wave" model in which linguistic changes spread like waves, leading ultimately to convergence. That is, growing similarity among languages that were initially quite different.
I: While divergence indicates tendency of differentiating languages, convergence means similarity of languages.
J: Right. Besides that, most linguists think primarily in terms of linguistic family trees. They find it necessary to construct some explicit models of how language change might occur according to a process-based view.
I: Have they formed some models?
J: So far, there are four main classes of models. The first is the process of initial colonization, by which an uninhabited territory becomes populated; its language naturally becomes that of the colonizers. The second are processes of divergence, such as the linguistic divergence arising from separation or isolation mentioned above in relation to early models of the Indo-European languages. The third group of models is based on processes of linguistic convergence. The wave model, formulated by Johannes Schmidt in the 1870’s, is an example. But convergence methods have not generally found favors among linguists.
I: What is the fourth class?
J: The slow and rather static operation of these processes is complicated by another factor: linguistic replacement. That factor provides the basis for a fourth class of models. In many areas of the world the languages initially spoken by the indigenous people have come to be replaced, fully or partially, by languages spoken by people coming from outside.
I: Just like American Indians hardly use their original language right now. They speak English, instead.
J: Yes. Anyway, if this large complicating factor was not discovered, the world’s linguistic history would be described by the traditional view of an Ur-language, followed by the gradual, long-term workings of divergence and convergence. So linguistic replacement also has a key role in explaining the origins of the Indo-European languages.
I: I quite agree. Well, Joanna, thank you for giving us so much information on the origins of Indo-European languages.
J: My pleasure.
I: Next week, we will have Professor Linda Smith from Oxford University to tell
us the development of English in recent decades. I will meet you then the same
time. Bye-bye.
6. What do linguistic family trees mainly indicate?
7. How many classes of models are there in the development of languages?
8. When did the wave model formulate?
9. Which factor provides the basis for the fourth class of model?
10. What does Joanna think of the linguistic replacement factor in explaining the origins of the Indo-European languages?