英语中关于by+时间的介词短语,如何影响动词时态1\By the sith century B.C.,they were no longer used.2\By the end of Octorber,I had finished my project.两个都是by+时间的用法,为什么前一个不需要用过去完成时,而后

英语中关于by+时间的介词短语,如何影响动词时态1\By the sith century B.C.,they were no longer used.2\By the end of Octorber,I had finished my project.两个都是by+时间的用法,为什么前一个不需要用过去完成时,而后
英语中关于by+时间的介词短语,如何影响动词时态
1\By the sith century B.C.,they were no longer used.
2\By the end of Octorber,I had finished my project.
两个都是by+时间的用法,为什么前一个不需要用过去完成时,而后一个需要?

英语中关于by+时间的介词短语,如何影响动词时态1\By the sith century B.C.,they were no longer used.2\By the end of Octorber,I had finished my project.两个都是by+时间的用法,为什么前一个不需要用过去完成时,而后
by the 6th century BC是从公元前六世纪开始就不用了,表示的是过去发生的事,用一般过去时就行了
by the end of October是从过去某一时间到十月底,我完成了项目,是过去的过去,用过去完成时