Concept:A fall in the external value of a currency means depreciation in the foreign exchange market.
Explanation:To prevent the naira from falling, the government must reduce its supply or increase demand for it.
Using foreign reserves to buy the naira removes excess naira from the market.
This action raises demand for the naira and supports its external value.
Selling the naira or increasing spending would add more naira to the market and worsen the fall.
Thus, buying the naira with foreign reserves is the appropriate measure.
Answer:D. buy its currency with foreign reserve