What Is the Difference Between a Nominal Value and a Real

What is the difference between a nominal value and a real value?

A) A nominal value is measured in monetary units while a real value is measured in current dollars.
B) A nominal value is measured in market rates while a real value is measured in terms of exchange rates.
C) A nominal value is measured in units of constant purchasing power while a real value is measured in units of current purchasing power.
D) A nominal value is measured in current market prices while a real value is measured in base year prices.