The correct answer is A. 4.55%.
The formula for calculating the labor turnover rate according to the replacement method is:
(Number of workers leaving + Number of workers discharged) / Average number of workers during the period
In this case, the average number of workers during the period is (500 + 600) / 2 = 550.
The number of workers leaving is 5 + 20 = 25.
The number of workers discharged is 20.
Therefore, the labor turnover rate is (25 + 20) / 550 = 4.55%.
Option B is incorrect because it is the labor turnover rate calculated using the separation method.
Option C is incorrect because it is the labor turnover rate calculated using the accession method.
Option D is incorrect because it is the labor turnover rate calculated using the combined method.