In constructing a confidence interval estimate for the difference between two population proportions, we:
A. pool the population proportions when the population means are equal
B. pool the population proportions when they are equal
C. never pool the population proportions
D. pool the population proportions when the populations are normally distributed

The expected value of the difference of two sample means equals the difference of the corresponding population means:
A. the statement is correct under all circumstances
B. only if the populations are approximately normal and the sample sizes are large
C. only if the populations are normally distributed
D. only if the samples are independent