问题如下：
Which one of the following statements is incorrect regarding the margining of exchange-traded futures contracts?
选项：
A.
Day trades and spread transactions require lower margin levels.
B.
If an investor fails to deposit variation margin in a timely manner, the positions may be liquidated by the carrying broker.
C.
Initial margin is the amount of money that must be deposited when a futures contract is opened.
D.
A margin call will be issued only if the investor’s margin account balance becomes negative.
解释：
ANSWER: D
All the statements are correct, except d. If the margin account balance falls below the maintenance margin (not zero), a margin call will be issued.
选项c，为什么不是存放deposit呢？答案写的是open的时候，不是交易的时候呢
