It was not until sixty years ago that a method of extracting aluminum ore was found which could lead to a cheap large scale process. 译文：直到六十年前人们才发现一种开采铝矿石的方法，从而有可能从中得到一种成本低廉，大规模提炼的炼铝法。

【参考答案】

直到六十年前，人们才找到一种提炼铝矿石的方法，使铝得以进行大规模低成本的生产。