help me. identify following samples.. technique used. a) Cluster b) Convenience c) Stratified d) Systematic?

samples by naming the technique used.? a) Cluster b) Convenience Stratified d) Systematic
A) every tenth customer entering a health club is asked to select his or her preferred method of exercise
B) Divide the subscribers of a magazine into three different income categories and then select a random sample from each category to survey about their favorite feature.
C) Take sample of six Zip codes from the Minneapolis metropoitan region and use all the car dealerships in the selected areas. determine the number of new cars sold each month at each dealership
D) Determine the annual salary of each of the nurses that are on duty at the time you chose to interview at the hospital.