X Question 1 Score on last try: 0 of 1 pts. See Details for more. > Next question You can retry this question below Choose the most complete statement. When building a Level C CI for a population mean: a. If o is known, then: O you do a T-interval O you do a Z-interval with d.f.=n-1 you do a Z-interval you do a T-interval with d.f. =n-1 X b. If o is not known, then: you do a Z-interval O you do a T-interval with d.f. =n-1 O you do a Z-interval with d.f.=n-1 O you do a T-interval X