12. In the inference procedures used in this course, we have sometimes used the t distribution, and sometimes the standard normal distribution. Consider the following four statements that relate to these two distributions. I. In inference procedures for a single population mean a, the t distribution should be used when the population variance is known. II. The variance of the t distribution is greater than that of the standard normal distribution. III. The & distribution tends toward the standard normal distribution as the degrees of freedom increase. IV. The standard normal distribution is symmetric about 0, but the f distribution is not. How many of these statements are true? (a) 0 (b) 1 x(0 2 (d) 3 (e) 4