麻烦老师解释一下这道题，谢谢

同学你好，这道题是考查put–call–forward parity，他与put-call parity稍许不同，根据put-call parity，有CK=PS，CK就是fiduciary call ，protective put 是指long asset ，long put。

而对于put–call–forward parity，构建protective put 是指long put，long risk-free bond，long forward，这里我贴下原版书中对于 put–call–forward parity中protective put 合成的解释（Recall our put–call parity discussion and assume that Investor A creates his protective put in a slightly different manner. Instead of buying the asset, he buys a forward contract and a risk- free bond in which the face value is the forward price.  ）

那么combing a protective put with forward，相当于是long put，long risk-free bond，long forward，再put–call–forward parity，有CK=PF，这里的PF就是指long put，long risk free bond，long forward，所以 long put+long underlying+long forward=CK,也就是等于fiduciary call