3. Consider a bivariate regression model with coefficient standard errors calculated using the usual formulae. Which of the following statements is/are correct regarding the standard error estimator for the slope coefficient? (i) It varies positively with the square root of the residual variance ($) (ii) It varies positively with the spread of X about its mean value (iii) It varies positively with the spread of X about zero (iv) It varies positively with the sample size I (a) (i) only (b) (i) and (iv) only (c) (i), (ii) and (iv) only (d) (i), (ii), (iii) and (iv)