Which of these intervals are possible confidence interval estimates of a population mean given a sample mean of 42.8 feet and some confidence level? (Assume that the population standard deviation is known and that the sample size is fixed.) a. 37.8 feet to 47.8 feet b. 39.3 feet to 46.3 feet c. 40.0 feet to 45.0 feet d. 40.0 feet to 45.6 feet e. 40.3 feet to 44.3 feet f. 41.0 feet to 44.6 feet