Answer : Option B

Explanation :

Under a fixed exchange rate system, devaluation and revaluation are official changes in the value of a country's currency relative to other currencies. Under a floating exchange rate system, market forces generate changes in the value of the currency, known as currency depreciation or appreciation.
Devaluation is a monetary policy tool used by countries that have a fixed exchange rate or semi-fixed exchange rate. One reason a country may devaluate its currency is to combat trade imbalances. Devaluation causes a country's exports to become less expensive, making them more competitive in the global market.
Currency war, also known as competitive devaluations, is a condition in international affairs where countries seek to gain a trade advantage over other countries by causing the exchange rate of their currency to fall in relation to other currencies.

Devaluation of currency will be more beneficial if prices of exports remain constant.

After a devaluation, the new lower value of the domestic currency will make it less expensive for foreign consumers to obtain local currency with which to buy locally produced export goods, so more exports will be sold, helping domestic businesses. Further, the new exchange rate will make it more expensive for local consumers to obtain foreign currency with which to import foreign goods, hurting domestic consumers and causing less to be imported. The combined effect will be to reduce or eliminate the previous net outflow of foreign currency reserves from the central bank, so if the devaluation has been to a great enough extent the new exchange rate will be maintainable without foreign currency reserves being depleted any further.

Source : gkplanet.com