NO.PZ2015122801000057
问题如下：
Astrid is short 400 shares of ABC stock and the stock's current price is $95 per share. She wants to cover her short position if the price falls to $80.
Gail has 250 shares of BBC stock, which is trading at $86 per share, and he needs to buy another 150 shares if the price rises to $98. What orders should Astrid and Gail establish to meet their targets?
选项：
A.Astrid establishes stop buy at $80 and Gail establishes limit buy at $98.
B.Astrid establishes stop buy at $95 and Gail establishes stop buy at $86.
C.Astrid establishes limit buy at $80 and Gail establishes stop buy at $98.
解释：
C is correct.
Astrid should establish a buy order with a limit at 80 because she wants to buy stock to close out her short position if she can buy it at 80(or less).
Gail should establish a stop buy at 98 because this order will be executed only if the stock price rises to 98.
C是正确的。
本题考察的是股票交易术语的区别。
Stop buy(停止买入) 和 limit buy（限价买入）的最大区别是前者是一个有效性指令，而后者是一个限定成交价的指令. Stop buy是大于等于某股价成交；limit buy是小于等于某股价成交。
Stop buy意味着只要比该指令定的价格高，就要买入。在本题中，Astrid做空股票时的市场价格是95美金，如果用stop buy $80指令，由于市场价远高于80，指令会立即生效，则Astrid立刻被平仓，就达不到要的效果了。
如果用limit buy，则意味这只有到达80这个股价（小于等于），才会平仓，这才满足Astrid的要求。所以A，B都是错误的。
Limit buy同理，如果用limit buy 来实现Gail的愿望，当前股价86美金，那成交的就会是84美金到98美金之间的单，显然不符合Gail的要求。而stop buy是大于98才成交。C正确。
第一个人，他做空股票，那么不是应该在股票价格上涨到一定的点，止损买入才合算吗，股票价格越低对他不是越好吗，为什么还要设置下限？
第二个人，股票在涨，他想额外买一些，不也是应该有个上限吗？
