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.