Correct Answer: C

Bonds with embedded options (such as callable or puttable bonds, or mortgage-backed securities with prepayment risk) pose the greatest challenge in determining economic capital. This is due to their non-linear payoff profiles. The valuation and risk assessment of instruments with embedded optionality depend heavily on complex models, interest rate path simulations (e.g., Monte Carlo simulations), and assumptions about borrower/issuer behavior. In contrast, linear products like ordinary stocks and fixed-rate loans have simpler risk profiles that are much easier to aggregate mathematically when determining a bank's economic capital.