Our everyday encounters with language are so natural and so extensive that we rarely consider language as an object of sufficient interest to warrant study. Language is always there, and we make use of it automatically, often with conscious effort. On the surface, there【M1】______ is nothing particularly interesting about so commonplace a phenomenon with human language. In fact, it is widely believed that,【M2】______ because everyone knows a language, everything about language is known. Therefore, this is far from true. Since the use of language is【M3】______ so natural to all people, it may seem that language itself must be quite simple, perhaps consisting of many words but involves only a【M4】______ few principles that control pronunciation and the organization of these words with sentences. However, investigation demonstrates that a【M5】______ language is an extremely complex, highly abstract, and infinitely producing system linking meanings with sounds. We all know the【M6】______ system of our native language, and this knowledge lies far below our【M7】______ consciousness. We may be able to describe particular sentences that we hear and we are certainly able to produce and understand an unending variety of sentences, but the foundation of these abilities is a body of knowledge about our language that we cannot readily to explain.【M8】______ Observing an activity, even participating it, is not equivalent to【M9】______ understanding it. Many people are able to work arithmetic problems with large【M10】______ numbers without being able to describe the mental processes they have used in arriving at the answer. 【M1】