问题如下：
A portfolio manager wants to hedge his bond portfolio against changes in interest rates. He intends to buy a put option with a strike price below the portfolio’s current price in order to protect against rising interest rates. He also wants to sell a call option with a strike price above the portfolio’s current price in order to reduce the cost of buying the put option. What strategy is the manager using?
选项：
A. Bear
spread
B. Strangle
C. Collar
D. Straddle
解释：
ANSWER: C
The manager is long a portfolio, which is protected by buying a put with a low strike price and selling a call with a higher strike price. This locks in a range of profits and losses and is a collar. If the strike prices were the same, the hedge would be perfect.
课上没学过呀 可以是bull spread吗
