1During the week ____ he tried to collect materials for his

1.因为事情发生在过去,从tried可以看出.the week that followed相当于the following week
2.由as引导的从句,如果用which,要把句子拆开,中间加逗号.he is absent,which is often the case.
Google上有这样的例句：And,considering the eminent authorship of the Principles,where they adopt a CISG concept -- which is often the case -- the Principles would seem to be citable in CISG briefs as illustrative of probable CISG intent.
as is often the case.这是个很常用的结构,“经常是这样”,可熟记.
3.从句的引导词.有指代整个句子的作用.类似的例子有很多.比如,
As is told by author...正如作者所说...
As is often thought...人们常这么认为...