In regression analysis, consider an estimated quadratic model: Y = b0 + b1X + b2X2. Select the statement that is true for this model. Select one: a. The coefficient of X in this model can be interpreted as the change in Y corresponding to X increasing by 1 unit. b. The coefficient of X in this model can be interpreted as the change in X corresponding to Y increasing by 1 unit. c. According to the estimated model, if X increases by 1 unit, Y increases by (b1 + b2) units. d. A 2nd order model always models the relationship between Y and X better than a linear model does. e. None of the above