In each of the following studies, identify which sampling technique best describes the way the data were collected (or could be treated as if they were collected): simple random sampling, random cluster sampling, or stratified random sampling. For cluster samples identify the clusters, and for stratified samples identify the strata.
(a) All 257 leukemia patients from three randomly chosen pediatric clinics in the United States were enrolled in a clinical trial for a new drug.
(b) A total of twelve 10-g soil specimens were collected from random locations on a farm to study physical and chemical soil profiles.
(c) In a pollution study three 100-ml air specimens were collected at each of four specific altitudes (100 m, 500 m, 1000 m, 2000 m) for a total of twelve 100-ml specimens.
(d) A total of 20 individual grapes were picked, one from each of 20 random vines in a vineyard, to evaluate readiness for harvest.
(e) Twenty-four dogs (eight randomly chosen small breed, eight randomly chosen medium breed, and eight randomly chosen large breed) were enrolled in an experiment to evaluate a new training program.