What's the answer to this? Please provide an explanation as to why also

Part 1: Multiple Choice. Circle the letter corresponding to the best answer. 1. Other things being equal, larger automobile engines consume more fuel. You are planning an experiment to study the effect of engine size (in liters) on the gas mileage (in miles per gallon) of sport utility vehicles. In this study, (a) gas mileage is a response variable, and you expect to find a negative association. (b) gas mileage is a response variable, and you expect to find a positive association. (c) gas mileage is an explanatory variable, and you expect to find a strong negative association. (d) gas mileage is an explanatory variable, and you expect to find a strong positive association. (e) gas mileage is an explanatory variable, and you expect to find very little association