Use the standard normal distribution or the t-distribution to construct a 90% confidence interval for the population mean. Justify your decision. If neither distribution can be used, explain why. Interpret the results. In a random sample of 21 mortgage institutions, the mean interest rate was 3.56% and the standard deviation was 0.47%. Assume the interest rates are normally distributed. Which distribution should be used to construct the confidence interval? IDE OA. Use a t-distribution because the interest rates are normally distributed and is known. OB. Use a normal distribution because n<30 and the interest rates are normally distributed. OC. Use a normal distribution because the interest rates are normally distributed and is known. ✔D. Use a t-distribution because it is a random sample, is unknown, and the interest rates are normally distributed. O E. Cannot use the standard normal distribution or the t-distribution because o is unknown, n<30, and the interest rates are not normally distributed. Select the correct choice below and, if necessary, fill in any answer boxes to complete your choice. OA. The 90% confidence interval is (. ). (Round to two decimal places as needed.) OB. Neither distribution can be used t construct the confidence interval.