Identify the relevant population for the following research foci, and suggest the appropriate sampling design to investigate the issues, explaining why they are appropriate

a. A company wants to investigate the initial reactions of heavy soft-drink users to a new "all natural" soft drink.

b. A hospital administrator wants to find out if the single parents working in the hospital have a higher rate of absenteeism than parents who are not single.

c. The director of human resources wants to investigate the relationship between drug abuse and dysfunctional behavior of blue-collar workers in a particular plant.

d. A marketer wants to generate some ideas on how women differ from men in acquiring product knowledge about cars.