When personal interviewing involves inviting six to ten people to gather for a few hours with a trained interviewers to talk about a product service, or organization the method is called ?

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When personal interviewing involves inviting six to ten people to gather for a few hours with a trained interviewers to talk about a product service, or organization the method is called ?

A. Selective sponsorship
B. Probing
C. focus group interviewing
D. the Delphi method