Define I1 as an interaction variable created from two binary variables, D1 and D2. In a regression model containing only the variables D1, D2 and I1:

a. The coefficient on I1 is the effect of D2 on Y, holding all other independent variables constant.

b. The constant coefficient is the average value of Y.

c. The coefficient on I1 is the Y intercept term of the regression in the case that D1 and D2 both equal 1.

d. The constant coefficient is the average value of Y when D1 and D2 are both zero.