In which of the following scenarios would the distribution of the sample mean x-bar be normally distributed? Check all that apply.

a. We take repeated random samples of size 10 from a population of unknown shape.

b. We take repeated random samples of size 15 from a population that is normally distributed.

c. We take repeated random samples of size 50 from a population of unknown shape.

d. We take repeated random samples of size 25 from a population that of unknown shape.