What is a four-digit code used by the accounting system to monitor purchases?

The four-digit code used by the accounting system to monitor purchases is the RC/CC, which stands for Resource Code/Cost Code. This coding system helps to categorize and track specific expenditures within an organization, ensuring proper budget management and financial accounting. Each code corresponds to particular resources or cost categories associated with various procurement activities. By utilizing this standardized code, organizations can maintain clarity and accuracy in their financial reporting and analysis, making it easier to monitor purchases and assess budgetary compliance.

The other options represent different concepts or coding systems that do not specifically serve the purpose of monitoring purchases in an accounting context. For example, BAG refers to budget authority groups, EEIC pertains to equipment and en route costs, and PEC relates to the program element code, all of which are valuable in their respective areas but not specifically suited for tracking purchase transactions through an accounting system.