The false statement is B.

• Marking to market is not merely an agreement between a broker and a client; it is part of the futures exchange/clearinghouse process that settles gains and losses daily.
• A is true: long and short futures positions typically have the same margin requirements.
• C is true: brokers may impose higher margin requirements than the exchange minimum, but not lower ones.
• D is true: funds above the required initial margin are generally withdrawable.

Correct answer: B