$20.$ The average values for the uncertain inputs cannot be used in a decision model and therefore, the need for Monte Carlo simulation cannot be eliminated. This phenomenon is called the $"\_\_\_\_\_\_\_\_\_\_\_\_\_\_",$ which states that the evaluation of a model output using the average value of the input is not necessarily equal to the average value of the outputs when evaluated with each of the input values.

a$.$ random variate

b$.$ flaw of averages

c$.$ risk analysis

d$.$ All of the above