Identify the type of sampling (stratified, systematic, convenience, or cluster) that best describes each of the following cases: (a) Splitting the FHSU student population into classes (freshmen, sophomore, etc.) and the selecting 50 students from each class to participate in a study. (b) Looking through the student directory, and choosing to email surveys to every 100th person. (c) Randomly selecting 10 on-campus courses, and then surveying all students in these 10 classes.