Unit nouns are a very special class of words that are used to specify the quantities of the modified noun. They are especially useful when we want to indicate the plural notion of a mass noun. E.g. two pieces of paper/advice.
单单位名词，又称量词，是用于表明被修饰名词数量的特殊名词。当我们想表示一个质量名词的复数概念时，它们特别有用。比如：两张纸/两条建议（在英语中都是 pieces of）。
