When designed experiments are conducted in public school systems, researchers typically choose a particular district, and randomly select teachers of, say, fourth grade students in that district. The experiment is then conducted using all the students in the selected classes. Which type of sampling scheme is implemented?At a school fund raiser, the name of every person who attended was entered into a drawing. At the end of the evening, six names were selected to receive door prizes. Which type of sampling scheme was implemented? A special interest group is conducting a survey regarding wolves in Yellowstone National Park. To adequately gauge opinions on both sides of the political spectrum, the researchers took the list of registered Democrats and selected a simple random sample of 100 people. Then, they took a list of registered Republicans and selected a simple random sample of 100 people. Which type of sampling scheme was implemented?