When injections, such as investment or government spending, exceed withdrawals like savings or taxes, there is a net addition to the circular flow of income. This surplus in aggregate demand forces firms to increase production to meet the higher demand, which subsequently leads to an increase in national income through the multiplier effect.

As domestic income levels rise, the tax base expands. Because most modern tax systems are progressive, individuals and corporations move into higher tax brackets, and total tax revenue collected by the government increases. This is a standard leakage in the circular flow of income model.

Withdrawals, also known as leakages, represent the portion of income that does not return to the circular flow of domestic spending. This includes savings, taxes, and expenditures on imports, which reduce the total demand within the domestic economy.

The circular flow model illustrates the continuous movement of money, goods, and services between different sectors of the economy. Households provide factors of production to firms, which in turn produce goods and services for consumption. This cycle creates a continuous loop where income earned by households is spent on goods produced by firms, thereby sustaining economic activity and ensuring the ongoing circulation of resources throughout the entire national economy.

Injections are additions to the circular flow of income that do not come from households. These include investment (I), government expenditure (G), and exports (X). These components increase the total demand for goods and services within the domestic economy, independent of household consumption patterns.

While standard macroeconomic theory classifies taxes as leakages or withdrawals from the circular flow, this question's provided answer suggests they do not affect the flow. This contradicts standard models where taxes reduce disposable income and aggregate demand. The answer is preserved per instructions.

Injections (investment, government spending, exports) are components that increase aggregate demand. The provided answer 'D' states that injections always equal national income, which is incorrect; national income is determined by the equilibrium of total injections and total leakages. This answer key appears to conflict with standard macroeconomic accounting identities.

A deflationary gap occurs when aggregate demand is insufficient to maintain full employment. When injections (investment, government spending, exports) are less than withdrawals (savings, taxes, imports) at the full-employment level, the economy experiences a shortfall in demand. This leads to downward pressure on prices and output, creating a gap between the actual level of national income and the potential full-employment level.

In the circular flow model, withdrawals (or leakages) are funds that leave the active spending stream. Taxation is a primary withdrawal because it removes money from households and firms, transferring it to the government. Unless this money is returned to the economy through government spending, it reduces the total aggregate demand.

Injections are defined as external additions to the circular flow of income, such as investment, government spending, and exports, which increase aggregate demand. The provided answer 'D' claims injections decrease investment, which is conceptually incorrect as investment is itself an injection. This answer key conflicts with established macroeconomic principles.