An investor owns a share of stock worth $ 75 and buys a put option for a premium of $ 2 with a strike price of $ 65. What are the risk and return characteristics of the portfolio The:（）

A. portfolio has unlimited downside risk, but the upside potential is limited to $ 65.

B. portfolio’s downside risk is a price of $73, but there is no maximum to the upside potential.

C. portfolio’s downside risk is a price of $ 63, but there is no maximum to the upside potential.

细胞刀治疗帕金森病（PD）的手术指征有哪些？