A general rule of thumb among marketing researchers is to use first and then collect . a. external secondary data; internal primary b. datainternal primary data; external primary datac. primary data; secondary datad. secondary data; primary datae. observational data; questionnaire data

The answer is "Option d"

Explanation:

The rule of thumb allows you to speak with 100 people in your competition for each important subset. It is a sample, that can't be trimmed for a smaller audience, in this process, the secondary data  is used first then the primary data is used, and other choices, that can be listed as follows were wrong:

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