Which of the following statements is true about stratified sampling?

a. subsets of the population are first created so that each subset has a common characteristic, such as gender.

b. random sampling is done but only within each of the subsets of the population.

c. it qualifies as a probability sampling method and the data reflect a normal distribution.

d. it is ok to use statistical tools such as multiple regression and ANOVA to analyze the data.

e. all of the above are true.