4- (1 point) Which of the following is not a Social Welfare Function that satisfies all four properties of social welfare functions we saw in class: a) W(x1, x2, x3): x1+ x2+ x3 b) W(x1, x2, x3): x1+ 0.5*x2+ x3 Cl W(x1: X2; X3): min{x1, X2; X3} d) W(x1, X2; X3): X1+X2 - X3 9) W(X1r X2, X3): X1*X2*X3 fl W(x1: X2, X3): X1*X2+ X3