The correct answer is: D. Credit policy.
Open market operations are a monetary policy tool used by central banks to influence the money supply. They involve the buying and selling of government securities in the open market. When a central bank buys government securities, it injects money into the economy. When it sells government securities, it withdraws money from the economy.
Income policy is a government policy that seeks to control the level of income in an economy. It can be used to reduce inflation or unemployment.
Fiscal policy is a government policy that seeks to control the level of spending and taxation in an economy. It can be used to stimulate economic growth or reduce the budget deficit.
Labour policy is a government policy that seeks to regulate the labour market. It can be used to improve working conditions or increase employment.
In conclusion, open market operations are a monetary policy tool used by central banks to influence the money supply. They are not part of income policy, fiscal policy, or labour policy.