试题题干
Word Formations
Complete the following sentence with the proper form of the word in the bracket.
(vain) Before they fled the country, the enemy 
attempted to destroy all the factories.
参考答案
试题解析
此处缺少副词。
attempted是动词，副词修饰动词。所以变vain为副词vainly。
句意：在他们逃离国家之前，敌人徒劳地试图摧毁工厂。