Astudent places an open hardcover book face down on a table. slowly, he pushes the two halves of the book toward each other. which geologic process is he trying to model? a. mountain building b. sediment deposition c. sea-floor spreading d. divergent plate boundaries

In an experiment examining the effects tai chi on arthritis pain, callahan (2010) selected a large sample of individuals with doctor-diagnosed arthritis. half of the participants immediately began a tai chi course and the other half (the control group) waited 8 weeks before beginning. at the end of 8 weeks, the individuals who had experienced tai chi had less arthritis pain that those who had not participated in the course.