情况下which才可以用that来代替。
The resistance of a conductor also depends on the substance it is made of. Like the sun, water is one of the necessities plants cannot go without. 3.特殊的省略场合
在以下一些名词后经常省略关系副词或“介词+which”；也可用关系副词that来引导定语从句。
the time/moment/instant/point/period/interval/cycle… the way/manner the reason the distance the direction the amount
the number of times/units/places/days… This, apparently, is the way the world is.
Work is the product of the force and the distance a body moves.
介词+which引导定语从句
介词+which引导定语从句，置于定语从句的开首，which不能省略。 that前不能有介词
某些在从句中充当时间、地点或原因状语的“介词+关系词”结构可以同关系副词when和where互换。
This is the house in which I lived two years ago. This is the house where I lived two years ago.
Do you remember the day on which you joined our club? Do you remember the day when you joined our club?
1. “介词+which”在从句中作状语
The age at which young people are allowed to drive any vehicle should be raised to at least 21. The settlers were unprepared for the long and patient toil by which alone the soil would be made to yield crops.
移民者对从事漫长而艰辛的劳作毫无准备，只有依靠这一点，土地才能出产粮食。 Most journalist learn to see the world through a set of standard templates into which they plug each day’s events.
多数新闻记者都学着用一套标准的模式去看待世界，并把每天发生的事件纳入这种模式。 注意：
该结构中介词的正确选择方法：
a. 由从句中的动词、形容词或名词确定
Copper is one of the metals with which we are most familiar.
How to live longer is a question to which man has tried to find a good answer for thousands of years.
b. 由被修饰的词所确定：
One of the great advantages of AC is the ease with which its voltage can be changed. The frequency depends on the purpose for which the device is designed. c. 根据整个句子所要表达的含义来确定
The substance in which there are many electrons is a good conduct.
注意下面“短语介词+which”的情况，常见的有： in terms of which by means of which as a result of which with respect to which according to which in accordance with which on the basis of which because of which by virtue of which by the help of which relative to which
Chemistry deals with changes as a result of which it is possible to form a new substance.
2. “介词+which”在从句中作定语
“Parallel”is used here to refer to two straight lines, the distance between which remains the same.
3. of which 在从句中作状语。Of与从句中的少数动词或形容词构成固定搭配。 consist of be built of
be composed of capable of
be made of aware of be constructed of sure of
A compound usually shows properties different from those of the elements of which it is made up.
of which 在从句中作定语
I am particularly grateful to the editors of the series of which this book is a part. He gave me some oranges, two of which were green. one of which… each of which… some of which… many of which…
all of which… none of which…
the first of which… the most important of which…
as引导的定语从句
as引导限制性的定语从句
这种定语从句只能修饰其前面的某个名词或代词。as意为“像。。。那样的”，它往往可与其前面的the same, such, as搭配使用。
He will repeat such questions as are discussed in the book. Such a student as works hard will be sure to succeed.
They made the same mistake as others would have made on such an occasion. He tried to make as few mistakes as he could avoid.
The sun gives us as much energy every minute as mankind utilizes in a year. 太阳每分钟给予我们的能量相当于我们一年所使用的能量。
as引导非限制性定语从句
通常的情况是，as在从句中一般作主语或宾语。从句的位置灵活，可处在主句的前面，句中或句尾。这种从句修饰的是整个主句而不是修饰一个名词或代词。as有自己固定的词义，一般意为“正如。。。那样”。这类定语从句与由as引导的方式状语从句的主要区别在于as引导方式状语从句时其本身在从句中一般是不能作句子成分的。
（1997Text2）As is true of any developed society, in America a complex set of cultural signals, assumption, and conventions underlies all social relationships. 同任何发达国家一样，一系列复杂的文化特征，信念和习俗构成了美国所有社会交往的基础。 As was discussed in the previous chapter, the direction in which the body is moving is also important.
Startford-on-Avon, as we all know, has only one industry—William Shakespeare. 众所周知，埃文河畔的斯特拉特福镇，只有一种产业——威廉.莎士比亚。 The students were late for school today, as often happens to my brother. 有些表达已经固定下来： as is reported 据报道 as is known to all 众所周知 as is often the case 情况往往如此 as often happens 这种情况常常发生 as has been said before正如前面所讲 as is shown in the pictures 如图所示 as is seen from the chart 如图所示
as is vividly betrayed in the cartoon above…如卡通生动地表明 as the name shows/implies/indicates/suggests顾名思义 as is hoped正如所希望的 as is anticipated 正如所预料的 as is supposed 正如所料想的
注意：
as 和which引导非限制性定语从句时，都能指主句所表达的整个意思，且在定语从句中都能够作主语和宾语。但不同之处在于：
as引导的从句位置灵活，可以位于主句前面，中间或后面，而which通常指前面提到过的情况或事实，而不是后面提到的情况或事实，which引导的非限制性定语从句只能放在主句之后；as后若为is或was+过去分词构成的被动语态，is或was可以省掉，which中的is或was在同样情况下不可省；as引导从句时，有“为人所熟知，显然”的含义，which没有这个含义；as引导的从句往往表示一种附加说明，which引导的从句则为较重要的评说。 As we know, smoking is harmful to one’s health.
The sun heats the earth, which is very important to us. He may be late, in which case we have to wait for him.
由as引出的一种特殊结构（它实际上源于由as引导的限制性和非限制性定语从句） as+过去分词，介词短语，副词
这一结构可看成在as引导的定语从句中省略了某些成分，可译成“正如。。。那样”。 As pointed out in the last chapter, the emf of a battery is generated by the chemical action within it.
As in your country, we grow wheat in the north and rice in the south. As before, he went there on foot.