能解释一下为什么么？

问题如下：

What is the difference between buying a call and selling a put?

选项：

解释：

Buying a call gives a trader the right to buy an asset at a certain price in the future. Selling a put gives the other side the right to sell the asset at a certain price at a certain time in the future. Buying a call gives a payoff of max(S - K, 0) where Sis the stock price when the option is exercised and K is the strike price. Selling a put gives a payoff of min(S - K, 0). Margin has to be posted when a put is sold but not when a call is bought.