It was the enemys boast of impregnability that caused their own defeat.敌人自我吹嘘战无不胜,这最终导致了他们自己的失败....

n.攻不破，不受影响...

impregnability的音标：impregnability的英式发音音标为：[ɪmpreɡnə'bɪlɪtɪ]impregnability的美式发音音标为：[ɪmpreɡnə'bɪlɪtɪ]...