(a) \(E(u_i) = 0\) This is because, only if this is the case, the line will pass through the center of the sample points
(d) All Figure out on your own
(b) \(\beta_1 - \beta_2P + \beta_3 P^2 + u\) We need a squared-term, so that we get a U-Shaped graph
(a) Uni-directional This question is only about the direction of relationship between the variables; not the magnitude. Sir asked in the question the nature of this specified relationship. not what i would choose.