The economists are often seen to perform substitution of assumptions by unavailability of data, rather than conducting laboratory experiments for testing their theories.
Economists are such professional experts who are involved in the study of economies and have a deep knowledge of the matters related thereto.
They are generally concerned with the matters of use, creation, development, and presentation of data, which revolve around the economic issues.
Sometimes unavailability of data obligates the economists to substitute this with making relevant assumptions in order to perform an experimentation of their theories.
Hence, option D; economists substitute assumptions in case of unavailability of data.
Learn more about economists here:
https://brainly.com/question/13199035
#SPJ1