Identify the sampling method used.

(a.) A college administrator divides the student population into four classes: freshman, sophomore, junior, and senior She takes a simple random sample from each class and surveys the participants about student services on campus. (b.)A farmer divides his orchard into 50 subsections, randomly selects 4, and samples all the tries within the 4 subsection to approximate the yield of his orchard.

(c.)A radio station asks its listeners to call in their opinion regarding the use of U.S. forces peacekeeping missions.