1. Personal source: This is the most direct and common source of information, including relatives and friends, colleagues and experts.
2. Commercial sources: This kind of information mainly comes from enterprises and institutions, including market research reports, professional consulting companies and industry analysis reports.
3. Public sources: Information from public sources is released by the government, non-governmental organizations and educational institutions, including government announcements, press releases and academic research.
4. Network sources: With the popularity of the Internet, the Internet has become an important channel for obtaining information. Information from the Internet includes social media, blogs, forums, news websites and so on.