押题中出现的，答案解释为“the value of a put option increases as interest rates rise. At higher interest rates, the value of the underlying option-free bond (straight bond) declines, but the decline is offset partially by the increase in the value of the embedded put option, which is more likely to be exercised.” 不理解的是，根据Value of putable bond=value of straight bond+put option，如果等号左边value of putable bond下降，all else equal，为了使等式平等，value of put option不是应该下降吗？
