Synthetic Long Put

这里没有说以risk free rate lend吧，只是说借钱出去，买Bond其实就是把钱借给对方融资啊，本质是一样的。

这一题也没有说要用二叉树，而是说用二叉树估值出现市场上的put是高估的，所以要卖put

下面是kaplan题目，让用binomial model来作答。 认为卖stocks得到的钱要以risk free rate lend出去才会 lock the arbitrage profit. 请问老师，用这种方法解释跟bsm模型解释是否矛盾
Under the binomial model, if the Merrill put is overpriced in the market, Mulroney's most appropriate action is to write the put option and:
A)purchase stock and borrow.
B)sell stock and borrow.
C)sell stock and lend.
The Merrill put is overpriced in the market, so to profit we want to go short (or write) that put option ("sell high"). To then hedge this short put position, we need a synthetic long put option, which can be replicated by lending that is funded by short-sale of the underlying stock. (A long put option is equivalent to a short position in the underlying, plus lending.)

是BSM模型的解读，第二点，可以用融资的角度来解释。

call 相当于是借钱买股票，但借的钱不够，所以需要自己掏钱，这部分就是期权费

put  反过来，相当于卖空股票来买债券，同样的，卖空股票的钱不 足以 买债券，还需要自己 掏钱，自己掏钱的部分就是期权费。