For each of the following scenarios, identify which sampling method is used:

a. The State College is conducting a survey of student attitudes and opinions. The plan is to use the list of all registered students and randomly select 50 freshmen, 50 sophomores, 50 juniors, and 50 seniors to make up the sample.

b. A second option for the college survey (in part a) is based on the observation that the college accepts a large number of transfer students each year. As a result, the junior and senior classes are twice as large as the freshman and sophomore classes. To ensure that the sample reflects this difference in class size, the alternative plan is to determine the number of students in each class, then select a sample so that the number for each class in the sample is in direct relation to the number in each class for the entire college.

c. The County Democratic Committee would like to determine which issues are most important to registered Democrats in the county. Using the list of registered Democrats, the committee selects a random sample of 30 for telephone interviews.

d. A faculty member in the Psychology Department posts notices in classrooms and buildings on campus, asking for volunteers to participate in a human memory experiment. Interested students are asked to leave their names and telephone numbers.

e. An educational psychologist selects a sample of 40 third-grade children from the local public school, ensuring that the sample is divided evenly with 20 boys and 20 girls.