by which用法是怎样
by which用法：为相关介词加关系代词的用法，定语在定语从句中要充当宾语的成分。之所以用by which，是因为定语在定语从句中要充当宾语的成分。
by which time 意思是“（到）那时”“（到）这时”，通常是指到某个时间点，即它的先行词通常应是时间点。如：
We arrived at noon, by which time the demonstration was over.
我们是中午到的，这时游行业已结束。
扩展资料
介词+关系代词的用法：
1、根据与定语从句中动词的搭配来确定介词。
如： Water is the natural medium in which fish live.
水是鱼类赖以生存的自然环境。(注意搭配live in)
2、根据与定语从句中形容词的搭配来确定介词。
如： Physics is the subject in our school in which every student is interested.
历史是我们学校每个学生都很感兴趣的课程。
3、根据与先行词的搭配来确定介词。
如： This is our classroom, in the front of which there is a teacher’s desk.
这是我们的教室，前面有老师的讲台。
4、根据句意来确定介词的使用。
如： This is the book from which I got the story.
这就是那本书，从中我读到这个故事。
(由于句意含有“从……”的意思，所以用介词from) This I did at nine o’clock, after which I sat reading the paper. 九点钟时我做这事，之后我坐着看报。(由于句意含有“在……之后”的意思，所以用介词after)。
