**Explanation:**

* The buying and selling of treasury bills, government securities, and other securities by the Reserve Bank of India (RBI) is known as Open Market Operations (OMOs).
* OMOs are one of the important monetary policy tools used by the central bank to control the money supply in the economy and influence the interest rates.
* Through OMOs, the RBI either injects or absorbs liquidity from the banking system by buying or selling government securities respectively.
* When the RBI buys government securities from commercial banks, it releases funds into the banking system, leading to an increase in liquidity. This helps in easing the availability of credit and reducing interest rates, thereby stimulating economic growth.
* On the other hand, when the RBI sells government securities to commercial banks, it absorbs funds from the banking system, leading to a decrease in liquidity. This helps in tightening the availability of credit and increasing interest rates, thereby controlling inflation and preventing excessive credit growth.
* OMOs also play a crucial role in managing the cash reserves and liquidity of commercial banks. By buying government securities, the RBI provides a channel for banks to invest their surplus funds and earn returns. By selling government securities, the RBI absorbs excess liquidity from banks and helps in maintaining the desired cash reserve ratio (CRR) and statutory liquidity ratio (SLR) levels.
* OMOs are conducted through auctions, where the RBI announces the sale or purchase of government securities and interested banks submit their bids. Based on the bids received, the RBI decides the price and quantity of securities to be bought or sold.
* The frequency and size of OMOs are determined by the monetary policy stance of the RBI and the prevailing market conditions. The RBI closely monitors various macroeconomic indicators and uses OMOs judiciously to achieve its monetary policy objectives.

Therefore, the correct answer is option C) Open market operations.