Carlos Montoya works in treasury operations. Treasury operations are primarily responsible for managing a company's liquidity, cash, and financial risk. This includes ensuring the company has enough cash to meet its obligations and investing any excess cash in short-term, low-risk instruments. Let's evaluate the options: setting long-term investment objectives for Limelight: This is a strategic function typically handled by the board of directors, investment committee, or senior management, not day-to-day treasury operations. investing excess cash in very short-term arrangements, such as overnight loans: This is a core responsibility of treasury operations. It involves managing the company's cash position, ensuring liquidity, and making short-term investments to maximize returns on idle cash while minimizing risk. setting investment strategies for achieving investment goals: This is a strategic role, usually performed by an investment department or senior financial executives, not the operational treasury team. communicating current and expected rates of return on company investments to accounting: While treasury provides data, the primary responsibility for financial reporting and communication to accounting typically lies with the accounting department or the CFO's office. Therefore, investing excess cash in very short-term arrangements is the most likely responsibility of someone in treasury operations. The final answer is $\boxed{\text{investing excess cash in very short-term arrangements, such as overnight loans}}$