先请看例句：
I called him by the wrong name, for which mistake I apologized.
这里的which是关系代词，作抽象名词mistake的限定词，相当于指示限定词(this、that、these、those)。从含义上判断，which mistake的先行词是this mistake。注意，虽然介词for因为关系词还是被提前了，但它的宾语不是which而是mistake。
类似的抽象名词先行词还有：fact, case, event, situation, time, failure, claim, point，mission等。这个抽象名词是用来总结整个主句情况或句子部分内容，而which用来作该抽象名词的限定词，这样就和主句发生了关联。关系限定词which引导的关系分句是非限制性的。所有这些用法大都只用于正式语体。
I called him by the wrong name, for which mistake I apologized.
我叫错了他的名字，因此，我向他道歉。
The traffic might be very busy now，in which case we may be considerably delayed.
现在的交通可能很繁忙，如此一来，我们可能会耽搁很久。
He is old,which fact is important.
他老了，这个事实很重要。
He went to America in 1980 ，by which time the Cultural Revolution has just ended.
他一九八零年去了美国，那时文化大革命刚刚结束。
She may be late, in which case we ought to wait for her.
她可能迟到了，在这种情况下我们应该等她。
He lost his temper, at which point I decided to go home.
他发脾气了，这样我决定回家。
He may have acute appendicitis, in which case he will have to be operated on.
他可能得了急性盲肠炎，如果是这样，他就得动手术。
He was appointed Lord Chancellor, in which post he spent the rest of his life.
他被任命为大法官，在这个职位上度过了他的余生。
They remain in the pouch for some seven weeks, by which time they are about 10cm long.
它们在育儿袋中停留了大约七周，到那时它们大约有10厘米长。
I was told my work was unsatisfactory, at which point I submitted my resignation.
有人告诉我，我的工作不令人满意，于是我递交了辞呈。
Sometimes you may feel too frail to cope with things, in which case do them as soon as it is convenient.
有时你可能会觉得身体太虚弱，无法处理事情，在这种情况下，只要方便就尽快处理。
We traveled together as far as Paris, at which place we parted company.
我们一起远赴巴黎，在那里我们分道扬镳。
It stormed all day, during which time the ship broke up.
狂风暴雨了一整天，在此期间船抛锚了。
They were on holiday from Lancashire, to which country they belonged.
他们从他们所属的兰开夏郡来度假。
Call again at eleven, by which time the meeting should be over.
十一点再打电话，那时会议应该结束了。
Ten years of hard work changed her greatly, for which reason he could hardly recognize her at first sight.
十年的辛勤工作使她大为改变，因此他一眼几乎认不出她来。
Water boils at 100℃, at which temperature it changes to gas.
水在100℃时沸腾，在这个温度下它变成气体。
Jane spent four years in college, during which time she studied medicine.
简在大学里呆了四年，期间她学习了医学。
He may come, in which case I'll ask him.
他可能会来，在这种情况下我会问他。
He emigrated in 1984, at which time there was much hardship and unrest in Europe.
他于1984年移民，当时欧洲充满了困难和动荡。
It rained all night and all day, during which time the ship broke in pieces.
雨下了一天一夜，在这期间，船摔成了碎片。
I will return at 3 pm, by which time(=when) I expect this room to be tidy.
我将在下午3点回来，那时我希望这个房间是整洁的。
This form of land-taking was characteristic of Wales rather than England, in which country the main settlement was over the low moorlands of Cornwall.
这种形式的土地征用是威尔士而不是英格兰的特点，在英格兰，主要的定居点位于康沃尔的低地。
This campaign lasted one year, during which time he and his deputies raged through the countryside.
这场运动持续了一年，在此期间，他和他的副手在农村到处穿梭。
They were under water for several hours, from which experience they emerged unharmed.
他们在水下呆了几个小时，从这次经历中，他们安然无恙地浮出水面。
The tourists visited the Royal Mint, in which place (=where) English coin is produced.
游客们参观了英国皇家铸币局，那里出产英国硬币。
The report contains statements the factual truth of which/whose factual truth is doubtful.
该报告所载陈述的事实真相令人怀疑。
The plane may be several hours late, in which case there's no point in our waiting.
飞机可能晚了几个小时，在这种情况下我们没有必要等了。
The speaker paused to examine his notes, at which point a loud crash was heard.
演讲者停下来检查他的笔记，这时听到一声巨大的撞击声。
Ten years of hard work changed her greatly, for which reason he could hardly recognize her at first sight.
十年的辛勤工作使她大为改变，因此他一眼几乎认不出她来。
The questions were all on opera, about which subject I know nothing.
那些问题都是关于歌剧的，我对歌剧一无所知。
反反复复研习以上例句，就能轻松掌握which的这个特殊用法句型，主动秀在作文里，作文自然上档次会多得一两分，这是什么概念自己想。