单词theretofore
adv.: 那时以前网络: 直到那时;在那以前;到那时为止
那时以前,直到那时
they had not done any work theretofore.
知道那时他们都没完成任何任务。
and introduced an element of strength and flexibility theretofore unachievable.
介绍了一种元素相关的强度和韧性不成立。