Answer:
b. are usually composed of diagrams and equations.
Explanation:
Economic models involve huge number of factors for their study and analysis.
It encompasses the analysis of various situations in an economy. It amounts for significant influence on the changes in market and environment, in which an economy runs.
Since it is complex in nature it involves huge diagrams, metrics, equations.
As with just theory it is not easy to form the understanding of economics. Thus, it involves many pictorial representations in the form of diagrams, graphs, etc:
Therefore, correct statement is
Statement b
