Final answer:
The core component of supply-side economics is economic deregulation, with the goal of lowering barriers to production to stimulate economic growth.
Step-by-step explanation:
A fundamental element of supply-side economics is economic deregulation and specifically, a reduction in tax rates. This approach suggests that by reducing the barriers to production, such as high tax rates and strict regulations, businesses and individuals will be incentivized to produce more goods and services. This increase in supply, in turn, is believed to stimulate economic growth. President Reagan's economic policies in the 1980s, which included substantial tax cuts, were driven by the belief that reduced income taxes would encourage people to work harder and increase the potential output of the economy, rather than merely boosting expenditure as per Keynesian economic theory.
The option that aligns with the core tenet of supply-side economics in the question provided is B. economic deregulation. Supply-siders advocate for policies that promote flexibility in production and investment, encouraging a greater supply of goods and services at potentially lower prices. Roosevelt's early ideas for a New Deal, which did not include supply-side economics, focused rather on public works and government regulation of the economy, among other things.