Which of the following assumptions is not needed for 3 to be an unbiased estimate of the population parameter in the regression model y = a + B₁x₁ + B₂x₂ + Ui where a is the intercept term, is the slope parameter, and u is the unobserved error Jerm? A. The variance of the error term is homoskedastic, i.e. var (u|x₁, x₂) = 0². B The variable, x₁ and x2, are mean independent of the error term. E[ulx₁, x₂] = 0. m C. No perfect collinearity D. We have a random sample of size n from the underlying population