A normal population has a u = 50 and o = 8. A random sample of n=4 scores from this population has a mean of 54. What is the z-score for this sample mean? O a. 0.5 O b. 1 OC. 2 O d. -0.5 Clear my choiceWhen a random sample is selected from a population, the sample mean is not expected to be exactly equal to the population mean. On average, the size of the difference between the sample mean and the population mean is predicted by O a. the standard error O b. the expected value O c. the mean of the population O d. the standard deviation of the population Clear my choice