In a study on weight gain in rabbits, researchers randomly assigned rabbits to 1, 2, or 3 mg of one of dietary supplements A or B (one rabbit to each level of each supplement, which is not enough, of course). Consider the linear model y = 0 1x1 2x2 3x3 i, where x1 is the dosage level of the supplement, and x2 is a dummy variable indicating the type of supplement used