Assign 13. Let X1, X2, ...., Xn is a random sample from the Normal population with parameters O and 9. Which of the following is a pivotal quantity? a. X b. X - 0 Vn(X-0) C. 3 d. Assign 14. The mean and standard of the heights of 50 high school boys of about the same age in a local high school are 63.4 and 7.0 inches, respectively. Compute a 99% confidence interval for the true average height of all boys in that high school