The theory that learning increases the efficiency of production is called the:
a. learning curve
b. learning effect
c. education cost
d. none of the above

A. learning curve 

Theory relates to a model in science because it presents the possible paradigms and patterns of the said concept and fact. It explains and elaborates the phenomenon of why it happened, how it happened and the factors that are invovlved in the process. A theory is a possible explanation of certain occurence. 
in addition, any time a scientific theory is challenged, it means it's not a good theory. And this statement is not valid. In theoretical models, they are revisited when there are further studies and discoveries found in a certain area where they can be remodeled and reintegrated instead of disregarding its credibility. Models, theories and paradigms are not challenged but rather encouraged, they are supported in many studies since these theories and models were created in order for us to understand a certain phenomenon but it would likely help the scientific society to be updated in the new forms or spheres of improvement rather than discouragement.