When Conducting a Two-Sample Test of Proportion Differences, What Must

When conducting a two-sample test of proportion differences, what must be calculated first in order to obtain a value for the standard deviation of the sampling distribution?

A) P_u: an estimate of the overall population proportion
B) Z (obtained) : the test statistic used to evaluate the null hypothesis
C) Z (critical) : the area on the x-axis of the curve demarcating the critical region
D) alpha: the threshold of error deemed appropriate for the test