Patrick is at Murphy's Pub when he sees a short man wearing a green suit, top hat, and buckled shoes. Also, the man is carrying a pot of shiny gold. Based on what Patrick knows about leprechauns and how they act, he assumes this fellow must be a leprechaun, too. Patrick has used a(n) heuristic to make his inference.

Which statement is a good description of a model? a) models are a description of nature based only on one or two variables. b) models are testable ideas but they are not very to most people. c) models are a description of nature that predicts more accurately than real events. d) models are an approximiation of a real system that omits all but most essential variables in a system.