A machine is supposed to put 13 oz of cereal in each box with a population standard deviation of 0.5 oz. 40 boxes are taken with the results shown below: 12.985, 12.755, 13.029, 13.073, 1__. What value completes the dataset?
A) 13.031
B) 13.035
C) 12.998
D) 13.004