What makes up the global economy?

Why did lincoln inform the confederacy that he would not e sending troops or weapons as food supplies were sent to fort sumter?

The economy of the united states is best described as

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.