during which time等于during when,用以引导非限制性定语从句，属于介词+when/where引导定语从句的范畴。
    如果作为先行词的时间名词在主句、从句中都是作介词宾语，充当时间状语，但介词前后发生了变化，那么，定语从句的引导词就要使用“介词+ when /which time”（介词的使用要取决于从句中的搭配需要）。
    如果作为先行词的时间名词在主句中作主语、宾语（作介词宾语时，主句从句中的介词是同一个介词）、表语等，加上适当的介词后在定语从句中时间状语，那么引导词就要使用“介词+which”（介词的使用要取决于从句中的搭配需要）。
①They stayed with me for two weeks, ____they drank all the beer I had.

A. for which B. which time C. during which time D. during which
②The book was written in 1946, ___ the education system has witnessed great changes.
A. when B. since which
C. since then D. since when

有类似用法的还有“介词+where":
① He stood at the window, ____ he could see what was happening.
A. from where B. from which C.which D. at which
② His head soon appeared out of one of the second storey window, from where he could see nothing but trees． 

1. I don't have to worry about the old age during which I even can't take care of ... 

2. The average length of labor during which these women received their meperidine was under 12 hours. 

3. 

US Congress: HR 1347, To extend the period during which members of the Armed Forces deployed in contingency operations may request and ...

4. Socially Awkward Situations During Which It Would Be Acceptable to Mess With Texas.

5. Fish evolve a longer lifespan by evolving a longer period during which they reproduce. 



1. In this post, he share his experiences during the past 5 years at learndirect, during which time they have strategically adopted a range of open source ...

2. Entered the service a fourth time some time in the year 1781, as a volunteer under Colonel William Moore and served about one month during which time he was ...

3. They lay there for three weeks during which time they made friends with the ... 

4. Have been fostering for five years, during which time they have fostered 20 children. 

5. ... registry will occur on 9/24/2006 from 9 PM to 9:45 PM EDT, during which time you will be unable to register, renew or manage .



during which的 中心语（先行词）大部分是表示时间段的名词例如 period 等；
而 duiring which time 的中心语（先行词）常常是具体的时间如 5 years 等。