C
Explanation:
Structured interviews (C) involve predetermined questions and a standardized approach, giving the researcher the most control over the interview process. This method is useful when consistency and comparability across participants are essential.
On the other hand, case studies (A) are more flexible and context-dependent, allowing for a greater degree of variability in the research process.
Unstructured interviews (B) are open-ended and flexible, providing participants with more control over the direction of the conversation, and semi-structured interviews set a balance between predetermined questions and participant-led discussions, offering more flexibility than structured interviews.