A、It should only be attempted by experienced researchers. B、It may cause researchers to avoid publishing good work. C、It is curr

Criticism of research lays a significant foundation for future investigative work, but when students begin their own projects, they are likely to find that the standards of validity in fieldwork are considerably more rigorous than the standards for most library research. When students are faced with the concrete problem of proof by field demonstration, they usually discover that many of the "important relationships" they may have criticized other researchers for failing to demonstrate are very elusive indeed. They will find if they submit an outline or questionnaire to their classmates for criticism, other students will make comments similar to some they themselves may have made in discussing previously published research. For example, student researchers are likely to begin with a general question but find themselves forced to narrow its focus. They may learn that questions whose meanings seem perfectly obvious to them are not clearly understood by others, or that questions which seem entirely objective to them appear to be highly biased to someone else. They usually find that the formulation of good research questions is a much more subtle and frustrating task than is generally believed by these who have not actually attempted it.
Questions 16 to 18 are based on the passage you have just heard.
16. What does the author think about trying to find weakness in other people’ s research?
17. According to the passage, what is one major criticism students often make of published research?
18. What does the author conclude about preparing suitable questions for a research project?