【问】 1. Langston Hughes always seemed to know who he was， and helped one of the writers in the United States. (TOEFL，83.11)
 2. is a useful approach to the of in field.(TOEFL，84. 5)
 前面两道托福题的目的显然在于考核考生是否已掌握了knowledge为不可数名词这一基本知识(第一题中的those knowledges应改为that knowledge，第二题中的knowl-edges应改为knowledge)。但是下面的实例却把knowledge用作可数名词，这是怎么回事呢?
 Finally，a knowledge of statistics is required by every type of scientist for the analysis ofdata. (A Course in Basic Scientific English，P. 7)
 最后，为了对数据进行分析，统计学知识是各种类型的科学家所必须的。
 【答】 当knowledge泛泛地指“知识”时，它是个不可数名词，不能与不定冠词a(an)连用。例如：
 1. Knowledge is power. (Prov)
 知识就是力量。
 2. All knowledge comes to us through our senses... (EED)
 所有的知识都是通过我们的五官进入我们的大脑的……
 但是，当knowledge指一个人对某一具体事物或具体学科的知识时，可以与不定冠词a(an)连用(不管有无定语)：
 1. He has an extensive knowledge of English. (AEG)
 他有广博的英语知识。
 2. He has a wide knowledge of history. (JED)
 他有广泛的历史知识。
 3. A knowledge of languages is always useful. (PEG)
 关于语言的知识总是有用的。
 4. A knowledge of several languages essential to the study of comparative literaturebecause without one can read books translation. (TOEFL，73. 6)
 请做下面的英语试题：
 1. is a useful approach to the of in field. (TOEFL 1984.5)
 2. Many people agree that__good knowledge of English is a must in__interna-tional trade today.
 A. a;不填 B. the; an C. the; the D.不填;the(全国高考英语试题，96)