Final answer:
Borrowing is not one of the three major sources of federal revenue; the main sources are personal income taxes, social insurance taxes, and corporate income taxes, with personal income taxes being the largest.
Step-by-step explanation:
The option that is not currently one of the three major sources of federal revenue is "d. borrowing." The three primary sources of federal tax revenue are personal income taxes, social insurance taxes, and corporate income taxes. Personal income taxes represent the largest source of federal government revenue, but they still constitute less than half of the total federal tax revenue. Social insurance taxes fund programs like Social Security and Medicare. Corporate income taxes also contribute a smaller share to the total revenue. By contrast, borrowing is a means of financing government deficit, not a source of revenue.