Preview the PPT “5 搜集资料 ” and Chapter 3 of the textbook 《 学术 》, and answer the following questions by your own PPT . 1. What are the principles for data collection? 2 . How many sources of linguistic data are there? 3 . How many types of research are there ? 4 . What are the usual ways to collect data? (two groups’ work: observation and interview; questionnaire) 5. How do we evaluate source materials? (library research)