A random sample of records of electricity usage of homes gives the amount of electricity used in July and size (in square feet) of 135 homes. A regression was done to predict the amount of electricity used (in kilowatt-hours) from size. The residuals plot indicated that a linear model is appropriate. What units does the slope have?
A) Slope is kilowatt-hours per house.
B) Slope is kilowatt-hours per square foot.
C) Slope is square feet per house.
D) Slope is square feet per kilowatt-hour.
E) Slope is houses per kilowatt-hour.