Read the following scenario and identify which type of sampling method is being used: A researcher is studying individuals at an elementary school which contains 30 different classrooms. The school contains 6 classes each of 5 different grades: 1st grade, 2nd grade, 3rd grade, 4th grade, and 5th grade classrooms, The researcher selects 8 classrooms at random. He then interviews each student in those 8 randomly selected classes for his research