What have been constructed for Operations Research problems and methods for solving the models that are available in many cases?

Answer: Option C

Mathematical Models have been constructed for Operations Research problems and methods for solving the models that are available in many cases. A mathematical model can be defined as a description of a system using mathematical concepts and language to facilitate proper explanation of a system or to study the effects of different components and to make predictions on patterns of behaviour (Abramowitz and Stegun, 1968).