D is corrent. Of the four alternatives only expected value uses probabilities as weights in determining the probability of outcome. Each possible outcome is multiplied by an appropriate weight (probability). These are then summed to determine the expected value.
A is incorrect because the coefficient of variation is the standard deviation divided by the expected value.
B is incorrect because the standard deviation is the square root of the variance.
C is incorrect because the objective function is a decision model which quantifies a goal.
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