It’s C, mostly by process of elimination.
A is instantly discardable because American dollar bills are not metal.
B is discardable because the opposite is true. Money must be available in limited amounts because scarcity is what gives currency value.
D is instantly discardable because not all countries use the same currency. A US dollar is not a Euro.
C is correct because money must be easily transferable, or it cannot be easily spent. If you cannot spend/use/transfer a currency, it has no value.