NO.PZ2018062007000080问题如下： If a call option is priced higher than the binomial model predicts, investors can earn a return in excess of the risk- free rate by:选项：
A.investing at the risk- free rate, selling a call, and selling the underlying.
B. borrowing at the risk- free rate, buying a call, and buying the underlying.
C.borrowing at the risk- free rate, selling a call, and buying the underlying. 解释：C is correct. If an option is trading above the value predicted by the binomial model, investors can engage in arbitrage by selling a call, buying shares of the underlying, and funding the transaction by borrowing at the risk- free rate. This will earn a return in excess of the risk- free rate.中文解析：在二叉树定价模型下，现在认为call被高估了，那么就要short call，同时long一份复制的call。低买高卖进行套利。而选项中borrowing at the risk-free rate and buying the underlying，也就是借钱买股票就可以复制出一个call，这样我们可以通过卖出一个被高估的call，买入一个合理定价的call来获利。为什么要short call 就要同时long一份复制的call？为什么borrowing at the risk-free rate and buying the underlying是借钱买股票的意思？借钱买股票怎么复制出一个call呢？}