25 In the model E(Y) =+P,X+BZ. where Z is a dummy variable,

a) The qualitative predictor has two categories.

b) One line has slope B, and the other has slope .

c) is the difference between the mean of Y for the second and first categories of the qualitative variable.

d) is the difference between the adjusted mean of Y (controlling for X) for the second and first categories of the qualitative vanable