a. true
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.