1. 研究目的与意义（文献综述包含参考文献）

1.introduction

1.1 research background

vocabulary has always been an important cornerstone of english writing and works as the fundamental building materials of language, thus vocabulary knowledge is one of the essential parts of sla (second language acquisition). as mccarthy stated that no matter how much the students learn grammar, no matter how successfully they master the pronunciation, without words to express a wider range of meanings, communication in a foreign language just cannot happen in any meaningful way (mccarthy, 2007). so vocabulary knowledge has aroused great attention of many scholars, teachers and students. research on lexical richness has become increasingly popular among researchers and correspondingly has produced interesting findings. and under the background of new curriculum reform, the ability of language output has been an important part in second language teaching. in their research, laufer and nation (1995) hold that a well-written composition which aims to impress readers must make full use of vocabulary.

2. 研究的基本内容、问题解决措施及方案

methodology

research questions

this paper studies the differences in the richness of vocabulary use in the compositions of english learners of different levels. it will focus on two dimensions of lexical richness, that is, lexical variation and lexical sophistication. this study mainly compares the change trends of lexical variation and lexical complexity between two groups of efl learners. the participants of study are the writing of chinese english major students. by studying this, the research is aimed to answer the following three questions: