short头寸是卖为啥还要交保证金呢

问题如下：

Due to the requirement of the exchange, the investment on wheat futures need $2000 initial margin and $1500 maintenance margin. An investor short a wheat future contract at $216, in which each future contract includes 100 tons. After one day, the future contract has risen to $222. Which of the following is the amount of the variation margin at the end of the first day?

选项：

$0.

$100.

$500.

$600.

解释：

D is correct

考点：Managing Credit Risk

解析：该投资者进入了卖空合约，当期货价格上涨的时候，投资者会面临亏损，金额为 ($222 - $216)×100 = $600

保证金账户会从$2000下降到$1400，这时低于最低要求的$1500, 因此为了保证不被平仓，需要将保证金账户补缴到初始保证金水平，因此要补充$600进入保证金账户。