How is it possible to make a profit from buying and selling currency?

a. the value of currency always stays the same, but you can exchange money for currency that is more valuable to make a profit.

b. the value of currency changes over time, so you can buy a country’s currency when its value is low and sell it when it is higher.

c. the value of currency changes over time, so you can buy a country’s currency when its value is high and sell it when it is lower.

d. the value of currency is always going up, so you can buy currency, hold onto it, and then sell it later to make a profit.