The model contains dummy variables. O The model omits some important explanatory factors Question 2 2 pts Consider the following regression model y, Po+Pix, +4. If the first four Gauss-Markov assumptions hold true, and the error term contains heteroskedasticity, then O Var(x)=0 O Var(x) = 1 O Var(x)= a O Var(x)=0