Which of the following is not true regarding currency options?

a$.$ Similar to futures contracts, margin requirements are normally imposed on option traders.

b$.$ Currency options can be classified as either put or call options.

c$.$ Options are traded on exchanges, never over$-$the$-$counter.

d$.$ Although commissions for options are fixed per transaction, multiple contracts may be involved in a transaction, thus lowering the commission per contract.

e$.$ All of these are true.