1. University language: A corpus-based study of spoken and written registers;Biber,2006
2. Student grammar of spoken and written English;Biber,2002
3. Longman grammar of spoken and written English;Biber,1999
4. Developing presentation skills: A perspective derived from professional education;Boyd;English for Specific Purposes,1989
5. Cambridge Dictionaries Online. Available on October 15, 2015 at http://dictionary.cambridge.org/us/dictionary/american-english/.