In macroeconomic theory, what is the term for the policy of central banks purchasing long-term government bonds to inject liquidity directly into the financial system when interest rates are already near zero?

The question describes a specific monetary policy used by central banks: purchasing long-term government bonds to inject liquidity into the financial system when interest rates are already near zero.

• A. Quantitative easing (QE) is precisely this policy. Central banks use QE to lower long-term interest rates and increase the money supply when conventional monetary policy tools (like adjusting the short-term interest rate) are no longer effective because rates are already at or near zero.
• B. Fiscal stimulus involves government spending or tax cuts, not central bank bond purchases.
• C. Sterilisation is a central bank action to offset the impact of foreign exchange interventions on the domestic money supply.
• D. Open market operations is a general term for central bank buying or selling government securities. While QE is a type of open market operation, "Quantitative easing" is the more specific and accurate term for the described scenario of purchasing long-term bonds when rates are near zero.

The correct option is A.

• A. Quantitative easing

The final answer is $\boxed{\text{A. Quantitative easing}}$