Which of the following is an example of an observational study? (7 A political candidate calls every fifteenth person in the local phone book and asks them to respond to a 3-question survey. (7 A researcher testing a new type of fabric softener treats 3 towels with the new product and 3 towels with the best-selling brand. He then asks 100 subjects which towels they find to be softer. (7 A principal wants to test a theory that students who do yoga for 10 minutes every morning achieve higher test scores than those who don't. She asks the teachers in half of the homerooms to lead students through a daily yoga session. Then, she compares those students' test scores to the other students' scores. (7 A scientist wants to determine whether a food reward can decrease the amount of time it takes for a mouse to complete a maze. For one group of mice, each mouse receives a piece of cheese when it completes the maze. None of the mice in the other group receive cheese for completing the maze. The scientist records the time it takes for each mouse to learn the maze