In a multiple regression problem involving two independent variables X1and X2, what does it mean if the value of b1is 3.2?

A) The relationship between X1and Y is significant.

B) The estimated value of Yincreases by an average of 3.2 units for each unit increase of X1, holding X2constant.

C) The estimated value of Y increases approximately by 3.2 units for each unit increase of X2, holding X1constant.

D) The estimated average value of Y is 3.2 units when X1= 0.