A political campaign manager wants to test the effectiveness of a new advertisement featuring Candidate X. The campaign manager takes a random sample of 300 voters before the ad goes on air and another random sample of 250 voters afterward. In the "before" sample, 158 out of 300 voters say they support Candidate X, and in the "after" sample, 140 out of 250 voters say they support Candidate X. If P1​ is the proportion of all voters who support Candidate X after the ad is aired and P2​ is the proportion of all voters who support Candidate X before the ad is aired, which of the following is the correct standardized test statistic for H0​:P1​−P2​=0?

(a) 0.56−0.527
(b) ​​0.56−0.527​/√(0.56×0.44)/300​+(0.527×0.473)/250
(c) 0.56−0.527
(d) 0.56(0.44)/​300−0.527(0.473)​/250
(e) 0.56−0.527/√(0.56×0.44)​/250+(0.527×0.473)​​/300