The correct answer is D. Sales.
Sales is the major source of revenue of any business. It is the amount of money that a business receives from selling its products or services. Sales are typically recorded as revenue on the income statement.
Investment is the act of putting money into something with the expectation of making a profit. Investments can be made in a variety of assets, such as stocks, bonds, and real estate. Investments are typically recorded as assets on the balance sheet.
Advances are payments that are made in advance of goods or services being provided. Advances are typically recorded as liabilities on the balance sheet.
Loans are sums of money that are borrowed from a lender. Loans are typically recorded as liabilities on the balance sheet.
In conclusion, sales is the major source of revenue of any business. Investment, advances, and loans are not sources of revenue.