Scientists collect data on the blood cholesterol levels (milligrams per deciliter of blood) of a random sample of 24 laboratory rats. A 95% confidence interval for the mean blood cholesterol level μ is 80.2 to 89.8. Which of the following would cause the most worry about the validity of this interval?

(a) There is a clear outlier in the data.
(b) A stemplot of the data shows a mild right skew.
(c) You do not know the population standard deviationσ.
(d) The population distribution is not exactly Normal.
(e) None of these are a problem when using a t interval.