Consider the Tobit model: y* = xB + u, u ~ N(O, 02), y = max(y*, 0}, where we can observe (y, x). Suppose that (b, s2) are the maximum likelihood estimators of (B, 02) respectively. Then the model's fitted value is defined as a xb. b. xb/s c y-xb/s. d. none of the abave