Orthopedic surgery students compared two types of spinal surgery to determine if patients were able to return to their active lifestyles. They studied disc replacement and spinal fusion. Identify the response and explanatory variables. The response variable is the amount of activity the patients were able to do after surgery, and the explanatory variable is the type of spinal surgery. The response variable is the type of spinal surgery, and the explanatory variable is the amount of activity the patients were able to do after surgery. The response variable is disc replacement, and the explanatory variable is spinal fusion. The response variable is spinal fusion, and the explanatory variable is the amount of activity the patients were able to do after surgery