Which one of the following statements is incorrect regarding the margining of exchange-traded futures contracts?

(a) Day trades and spread transactions require higher 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 if the investors margin account balance drops below the mainte- nance level.