The correct answer is D. All of the above.
A mathematical model is a mathematical representation of a system. It is used to understand the system and to make predictions about its behavior. A mathematical model can be used to simulate the system, to optimize the system, or to control the system.
A mathematical model typically consists of three types of variables: uncontrollable variables, dependent variables, and decision variables.
Uncontrollable variables are the variables that are not under the control of the modeler. They are usually determined by the environment in which the system operates. For example, the weather is an uncontrollable variable in a model of a power plant.
Dependent variables are the variables that are determined by the uncontrollable variables and the decision variables. They are usually the variables that the modeler is interested in predicting. For example, the output of a power plant is a dependent variable in a model of a power plant.
Decision variables are the variables that are under the control of the modeler. They are the variables that the modeler can change to influence the behavior of the system. For example, the amount of fuel that is burned in a power plant is a decision variable in a model of a power plant.
In conclusion, all mathematical models generally comprise uncontrollable variables, dependent variables, and decision variables.