The following list presents the alternative samples obtained by a health care market- ing research firm for its clients. Describe the type of sample each represents.

(a) Ten people sitting in the waiting room are asked to describe the ambiance of the facility and the attitude of the receptionist.

(b) The medical school samples alumni regarding an evaluation of their edu- cation. Respondents are selected in an amount equal to the same population of specialties from the graduating class.

(c) The walk-in clinic calls every 15th patient who visited the clinic on Wednesday to assess whether the patient was greeted by the receptionist and given a handbook regarding the scope of services and an explanation as to how the clinic operated.