For each of the following research projects, list three variables for stratification of the sample. a. A nationwide study of motels and hotels is being conducted. An attempt will be made to determine the extent of the availability of online links for customers. A sample of motels and hotels will be taken. b. A consumer panel is to be formed by sampling people in Michigan. Members of the panel will be interviewed periodically in an effort to understand current consumer attitudes and behaviors. c. A large soft-drink company wants to study the characteristics of its U.S. bottlers, but the company does not want to conduct a census. d. The business analytics bureau of a large university is conducting a project in which the bureau will sample paper-manufacturing companies.