Derek recently bought a car and was told by the dealer that he should only use premium fuel. The dealer also told Derek that if he did not use premium fuel the car's fuel economy would drop. To see if this was true, over the period of a few months Derek filled his car with three different grades of fuel and recorded how many miles he was able to get out of each tank of gas under similar driving conditions. Derek is in effect performing an experiment that contains explanatory and response variables. Which statement best describes the explanatory and response variables involved in this experiment