Classify each study as an observational study or a designed experiment. - A group of patients is randomly divided into two groups. The first group gets the covid vaccine. The second group gets placebo. We compare the percentage of patients who get sick with covid. - Two sections of the same class are taught during a semester. Students randomly assign themselves to either section. A professor then teachers each section using a different teaching strategy. At the end of the semester, he compares the grades of the two groups. - A professor announces that he will be teaching an online class and a face-to-face class. Students decide which class to take. At the end of the semester the professor compares student performance in each class. - We survey a group of patients and ask them who got a covid vaccine shot and who did not. We then compare the percentage of people who got sick with covid in each group. - A survey was conducted that asked people which drink they prefer, Coke or Pepsi. - To see if people like Coke or Pepsi better, we randomly divide people into two groups. We give one group Coke and ask them