7. In which of the following situations is the calculation of the z-statistic NOT appropriate for making inferences about a single mean? a. The variable of interest is normally distributed in the population, (I is known, and 11 (number of observations) is large. b. The variable of interest is normally distributed in the population, 0' is known, and n is small. c. The variable of interest is normally distributed in the population, (I is unknown, and n is small. d. The variable of interest is not normally distributed in the population, (I is known, and n is large. e. Calculation of the zstatistic is appropriate in each of these situations