They had walked only about 500 meters ___ Mary felt great pain in her stomach.答案用when /before

来源：百度知道编辑：UC知道时间：2024/06/03 10:49:28

when：当Mary感到肚子剧烈疼痛时，她们才走了500米。
before：在Mary感到肚子剧烈疼痛之前，她们才走了500米。

从语法上来说，when和before都正确。
这里主要考的是过去完成时态。表示过去某一时间或动作之前已经发生或完成的动作或存在的状态。句中常用by， before， when， until等词引导的时间状语。它是以过去某一时间为起点，所以过去完成时是一个相对的时态，表示的是“过去的过去”。
语法上都正确但是意义不同，before含有在……之前的意思，when在这里是当……的时候。

用before，在他们刚走了500米后mary就觉得胃疼了。

我认为应是when

has walked .had walked ..have been walked.had been walked 1,Dinosaur K had ----------------legs and walked------------------. _______ experience they had! 英译汉-They had They had done that before after the stranger had just walked for tow minutes中had有什么用 After they had a rest, they went on ___ They had learned 3000 English words ____. They had a good preparation for the project,so they had little__all the work. The robber walked out of the bank, no one realized what had happened,not even 。