To do inferential procedures comparing two proportions, we need another variance formula (our ruler). This formula is based on what principle?

Question

A) The variance of the difference of two statistics is the difference of the variances of each statistic.
B) The variance of the difference of two statistics is the smaller of the variances of each statistic.
C) The variance of the difference of two statistics is the sum of the variances of each statistic.
D) The variance of the difference of two statistics is the larger of the variances of each statistic.