In every cultivated language, there are two great classes of words which, taken together, comprise the whole vocabulary. First, there are those words（1）which we become acquainted in daily conversation, which we（2）,that is to say, from the（3） of our own family and from our familiar associates, and（4） we should know and use （5 ）we could not read or write. They （6） the common things of life, and are the stock in trade of all who （7） the language. Such words may be called“popular”, since they belong to the people （8） and are not the exclusive （9） of a limited class. On the other hand, our language （10） a multitude of words which are comparatively （11） used in ordinary conversation. Their meanings are known to every educated person, but there is little （12） to use them at home or in the market-place. Our （13） acquaintance with them comes not from our mother's （14） or from the talk of our school-mates, （15） from books that we read, lectures that we （16） ,or the more （17）conversation of highly educated speakers who are discussing some particular （18） n a style appropriately elevated above the habitual（19） f everyday life. Such words are called“learned”, and the （20） between them and the“popular”words is of great importance to a right understanding of linguistic process.
请在19处填上正确答案（）
A.border
B.link
C.degree
D.extent