When using a two-sample z test for P₁ - P₂, why do we check that the number of successes and failures in both groups is at least 10?

a. So that the observations can be considered independent.

b. So that we can make an inference about cause-and-effect.

c. So that the distribution of both populations will be approximately Normal.

d. So that the distributions of both samples will be approximately Normal.

e. So that the sampling distribution of the difference in sample proportions will be approximately Normal.