4. A researcher wants to find a confidence interval estimate of the mean time it takes to complete an order over the phone at a call center for a large retail company. He has selected a random sample of 18 orders and recorded the time to complete the order. The sample mean time was 4.27 minutes and the sample standard deviation was 0.78 minutes. Assuming the conditions needed for inference are met, which of the following is the appropriate 98% confidence interval? (A) 4.27 + 2.326 0.78 V18 (B) 4.27+ 2.054 0.78 V17 (C) 4.27 + 2.552 0.78 V18 (D) 4.27 + 2.567 0.78 V18 (E) 4.27 + 2.567 0.78 17