前應該用an,例如:
1、They had welded a bunch of untrained recruits into an efficient fighting force.他們把一羣未經訓練的新兵組織成了一支有戰鬥力的部隊。
2、An efficient transport system is critical to the long-term future of London.高效的公共交通系統對倫敦長遠的未來至關重要。
3、An efficient bulb may lighten the load of power stations一個節能燈泡也許就能減輕發電站的負荷。