For each of the situations described, state whether the sampling procedure is simple random sampling, stratified random sampling, cluster sampling, systematic sampling, or convenience sampling. (a) All freshmen at a university are enrolled in 1 of 30 sections of a seminar course. To select a sample of freshmen at this university, a researcher selects 4 sections of the seminar course at random from the 30 sections and all students in the 4 selected sections are included in the sample.