Which of the following relates to revenue income?

The correct choice pertains to income generated from day-to-day operations, which is fundamentally linked to revenue income. Revenue income is defined as the income that a business earns from its core activities, primarily through the sale of goods and services. This ongoing stream of income reflects the company's primary business operations and is crucial for understanding its financial health.

In contrast, the other options refer to different types of financial activities. Sales of fixed assets involve selling long-term investments or physical items that the business owns, which does not contribute to revenue income generated through regular operations. Money received from loans pertains to financing activities rather than operational income, indicating an inflow of cash that must be repaid and is not an indicator of the company's operational performance. Lastly, capital gains are profits made from the sale of assets, but these gains arise from investment activities rather than the core operational activities of a business. Thus, the choice that focuses on income from day-to-day operations accurately describes revenue income and its significance in a business context.