Let X1, X2,... be i.i.d. random variables each with mean u and variance o2 < 00. Consider the Xn- sequence of random variables Y, Let X, denote the sample mean of X1,...,Xn- From the statements below, select those that are true in general, not just in some special cases. O a. At each fixed point y E R, the cdf of Y, evaluated at y approximately equals the standard normal cdf at that point, (y), with the approximation improving as n increases. O b. Y, has expected value approximately but not necessarily exactly equal to zero. The approximation improves as n increases. O c. X, has expected value approximately but necessarily exactly equal to u. The approximation improves as m increases. O d. Y, has variance equal to one for all n2 1. e. Xn has variance equal to one for all n >1.