Explanation

Devaluation lowers the foreign-currency price of exports and raises the domestic-currency price of imports, improving the trade balance through the Marshall–Lerner mechanism. However, if domestic prices rise at the same time — because imports are costlier or inflation is unchecked — the real exchange-rate advantage is eroded. When domestic goods prices remain constant, the competitive gain from devaluation is fully preserved and its benefit is maximized. The other options describe conditions (rising inflation, falling interest rates) that would dilute, not maximize, the gain.