A combination of document analysis, observation and interviews are applied usefully in 

(A) survey research 

(B) field experiment 

(C) case study 

(D) content analysis

Correct Ans: (C) 

Explanation:

A case study is a qualitative research method that provides a detailed investigation of a subject, event, or organization. Researchers use document analysis, observation, and interviews to gather insights. This approach helps in understanding real-life situations with depth and context.

For instance, researchers studying media influence may analyze news reports, observe audience reactions, and conduct interviews with media consumers. By using multiple sources, case studies ensure accuracy and reliability.

Additionally, this method allows for flexibility. Researchers can adapt their approach as new insights emerge. Unlike surveys, which focus on broad patterns, case studies provide rich narratives and detailed findings.

Moreover, case studies are widely used in journalism, business, psychology, and social sciences. They help researchers identify trends, test theories, and develop practical solutions.

In conclusion, case study research offers a holistic perspective by integrating multiple research techniques. It remains an essential tool for gaining in-depth knowledge on complex issues.