问题如下：
Tim owns 200 shares PZ company's stock. The current price of the stock is $20 per share. When use technical analysis, Tim finds that the stock price has a support level of $15. The support level means if the stock price is going downward, the support level will give the price a support and will make the price stay above the level rather than fall below it. Tim does not want to sell the stocks immediately, but he are concerned about the possibility of a huge loss if the stock price falls below the support level. Which of the following statements is correct?
选项：
A. Short sell order is most appropriately address Tim's concern.
B. Good-till-cancelled stop sell order is most appropriately address Tim's concern.
C. Good-till-cancelled stop buy order is most appropriately address Tim's concern.
解释：
B is correct.
To address Tim's concern, a good-till-cancelled stop sell order is the most appropriately order. If the stock price declines below $15, the order will be triggered. Sometimes, this order is referred to as a good-till-cancelled stop loss sell order. If the stock are generally bullished and has no sale signals, investors who short selling the stock would be expected a loss. When the stock price is increasing, a stop buy order is placed to buy the stock.
考点：Execution Instructions
这道题就是说一个投资者有200只股票，现在价格是每股20元，技术分析得到该股票的阻力位是15元（通常跌倒15元就会反弹）。但是如果股票真的跌破阻力位就会出现巨大亏损，投资者目前还不想卖股票，但他也担心出现跌破阻力位的情况，所以应该发布什么指令呢?
A就是一个正常的以市场价格卖空的指令，但题干明确说除非大跌TIM并不想现在就卖。
B:投资者现在拥有股票，希望在未来股票价格跌破15时卖出止损，这就是good-till cancelled stop sell order的作用，stop order是一个有效性指令，当价格触碰15才会执行卖出指令
C:stop buy不能解决TIM的顾虑，因为他持有股票担的是股票下跌而不能及时止损，而选项C是通常是卖空方用来止损的指令。
由于答案中“good-till-cancelled stop sell order”这样的指令比较难理解，如果指令的表达方式不是很多，可否穷举类似的指令，并加上中文翻译，让我们方便记忆
