The slope b of the population regression line describes

(a) the exact increase in the selling price of an individual unit when its appraised value increases by $1000.

(b) the average increase in the appraised value in a population of units when selling price increases by $1000.

(c) the average increase in selling price in a population of units when appraised value increases by $1000.

(d) the average increase in the appraised value in the sample of units when selling price increases by $1000.

(e) the average increase in selling price in the sample of units when the appraised value increases by $1000.