【正确答案】正确答案：A word that belongs to the closed-class is one whose membership is fixed or limited. New members are not regularly added. Therefore, pronouns, prepositions, conjunctions, articles, etc., are all closed items. The open-class is one whose membership is in principle infinite or unlimited. With the e-mergence of new ideas, inventions, etc. , new expressions are continually and constantly being added to the lexicon. Nouns, verbs, adjectives and many adverbs are all open-class items. However, the distinction between closed-class words and open-class words is not quiet as clear-cut as it seems. Preposition, though a closed-class, is relatively open one in English. Expressions such as "regarding", "throughout", "out of" are now recognized as prepositions or complex prepositions. In respect of open-class items, auxiliary verbs, which used to be ranked as open-class words, are relatively closed in number.