The Volume of Oxygen Consumed (In Liters Per Minute) While

Multiple Choice

The volume of oxygen consumed (in liters per minute) while a person is at rest and while a person is exercising (running on a treadmill) were both measured for 50 subjects. The goal is to determine if the volume of oxygen consumed during aerobic exercise can be estimated from the amount consumed at rest. The results are plotted below. In this study, the explanatory variable is:

A) the volume of oxygen consumed at rest.
B) the volume of oxygen consumed while running.
C) the instrument used to measure the volume of oxygen consumed.
D) either variable-it doesn't matter which is considered the response.