conomists make use of assumptions, some of which are unrealistic, for the purpose of a. teaching economics to people who have never before studied economics. b. advancing their political agendas. c. developing models when the scientific method cannot be used. d. focusing their thinking.

According to the give question, the economist use the various types of assumptions for understanding the various types of managing the business in the competitive market environment.

The economist assumptions is basically helps in making various types of effective decisions that makes better understand their client and also customer in the economic model.

Some of the assumptions are also unrealistic for the main purpose of focusing their thinking ability as it helps in improving the thinking ability of the person so that they can make various types of effective decisions.

Therefore, Option (D) is correct answer.