Scenario 1: A researcher at a nearby university wants to look at what teachers in a certain school district think about new policy changes. The researcher makes a list of all the schools in the district and uses a random number generator to select five schools from the district. Then the researcher interviews every teacher at each of those five schools. The researcher is using - in this study. Scenario 2: The campus safety committee has asked Professor Ibrahim to study bicycling on his campus. He trains two observers to rate the safety behaviors of cyclists at various locations around campus. He randomly selects 10 observation locations from the places where bicycles can be ridden on campus and randomly selects five 1-hour durations for each location. He has his observers make observations at each of the 10 places for each of the five durations. Dr. Ibrahim is using - . stratified random samplingsystematic samplingcluster samplingmultistage sampling