The world has approximately 3000 （some put it 5000） languages, which can be grouped into roughly 300 language families and on the basis of similarities in their basic word stock and ______.
【正确答案】：grammar
【题目解析】：本题考查第二章印欧语系的内容，需要对课本知识熟悉，划分300种是根据词汇和语法。
