Answer:
D. Obtain a cluster sample by randomly selecting 20 counties and visiting every restaurant within those counties.
Step-by-step explanation:
Since this executive wants to minimize cost and expenses he should use a cluster sample of 20 counties and using the selected counties as a representative of the whole. Cluster sampling is a good and useful way of doing market research. It is more economical than other sampling methods and as the executive cannot get information on the whole population, he would be able to get information from the clusters.