In which of the following cases is the assumption most reasonable ?

• A. To address the impact to taxes on income distribution an economist assumes that everyone earns the same income.
• B. To address the impact of money growth on inflation, an economist assumes that money is strictly coins.
• C. To model the benefits of trade. an economist assumes that there are two people and two goods
• D. To estimate the speed at which a beach ball falls, a physicist assumes that if falls in a vacuum.