问题如下：
The Black-Scholes-Merton option pricing model is not appropriate for valuing options on corporate bonds because corporate bonds:
选项：
A. have credit risk.
B. have an upper price bound.
C. have constant price volatility.
D. are not priced by arbitrage.
解释：
The Black-Scholes-Merton model cannot be used for the valuation of fixed-income securities because it makes the following assumptions, which are not reasonable for valuing fixed- income securities:
l There is no upper price bound.
l The risk-free rate is constant.
l Bond volatility is constant.
b选项是什么意思呢 为什么不选a
