According to the Goldgeier and Saunders reading, how have constraints on presidential authority in foreign policy eroded and what factors have caused this erosion?

Donald is studying the eating habits of all students attending his school. he samples the population by dividing the students into groups by grade level and randomly selecting a proportionate number of students from each group. he then collects data from the sample. which type of sampling is used? select the correct answer below: systematic sampling convenience sampling stratified sampling cluster sampling