by which引导定语从句
bywhich？
by which是什么从句？
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。
bywhich？
1.There are a number of distinguishing characteristics by which you can identify a Hollywood epic.好莱坞的史诗大片有着一些与众不同的特点。
2.There has been no yardstick by which potential students can assess individual schools before signing up for a course.有意就读的学生在报名参加一门课程前没有任何参照标准去衡量各个学校的水平。
at which在定语从句中的用法？
1、at which：在...，关系代词用作主语或宾语。
2、in which：在...里面，多用在书面语中。
3、on which：在...上面，由介词加上关系代词来引导。
4、for which：为了...，从句由介词加上关系代词来引导。
5、by which：用...，非限制性定语从句所修饰的是物。
6、from which：从...，非限制性定语从句所修饰的是整个主句。
by which time怎么用？
没有 by which time、in which time、on which time 这种用法，要么是副词短语 by the time (到这个时间为止)、in time (及时)、on time (按时)，或者是由 by which (截止到这个时间)、in which (在这段时间)、on which (在这个日子) 构成关系词引导定语从句，用来修饰表示时间的先行词名词。