In order for a prediction interval for y or a confidence interval for Myjx to be valid, which of the following must hold? a. The true relationship between the predictor variable x and the response variable y must be close to linear. b. The variability of the x-values must be about the same at each fixed y value. c. The variability of the y-values must be about the same at each fixed x value. d. The variability of the x-values and the y-values must be about the same. Select one answer (c) and (d) must hold B (a) and (b) must hold (b) and (d) must hold D (a) and (c) must hold