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 deviation σ.

d. The population distribution is not exactly Normal.

e. None of these are a problem when using a t interval.

Select the best answer.