Speculators Play an Important Role in a System of Floating

Speculators play an important role in a system of floating exchange rates because

A) to make a profit, they must buy a currency when its value is low and sell it when its value is high.
B) their purchases and sales lead to wild gyrations in exchange rates and thus increase instability.
C) they place additional risks on businesses that need to purchase and sell foreign currency.
D) All of the above are correct.