In a typical variable-rate loan, the extra interest yield owed by a borrowing company above the varying London Interbank Offering Rate (Libor) can be contractually set by the lender via the subtraction of the current spread between Libor and T-bill rates from: (a) the premium yield required for the default risk of the loan (b) the premium yield required for the systematic risk of the loan (c) the premium yield required for the transaction costs of trading the loan (d) the sum of all the above (c) the tax-adjusted premium yield on Libor loan indexes