We wish to develop a confidence interval for the population mean. The population follows the normal distribution, the standard deviation of the population is 3, and we have a sample of 10 observations. We decide to use the 90 percent level of confidence. The appropriate statistic for the level of confidence is:
A: z = 1.645.
B: z = 1.960.
C: t = 1.833.
D: t = 2.262.