Which of the following is the major source of income for commercial banks (except "money center" commercial banks) ?
A. Interest rate spread --- the difference between what banks earn from their assets (mainly interest) and what they pay on their liabilities (again mainly interest).
B. Fee income --- income generated by activities without putting banks' balance sheet at risk.
C. Capital gain --- profit by selling assets at a price higher than their purchase price.
D. None of the above