which与as在定语从句中的不同用法(2)
(3)当which引导的从句在意义上近乎并列关系时，可以用and this, and that代替，意思是“这件事”。
例 15 He changed his mind, which(and this, and that) made me very angry. 他改变了主意，这使我很生气。
而as主要起与上下文连接的作用，表达说话人的看法、观点，并指出主句内容的出处或根据等。
例 16 Einstein, as we know, is a famous scientist.爱因斯坦，众所周知，是一位伟大的科学家。
例 17 As is announced in today’s newspaper, we must improve our style of work. 今天的报纸上说，我们必须改进工作作风。
(4)做主语时，which既可以作系动词be的主语，也可以作实义动词的主语，而这时as 只可以做系动词be的主语。
例 18 He married her, which was natural. (可用as代替which)他和她结婚，这是很自然的事。
例 19 He won a /the Nobel Prize in chemistry, which made him illustrious. (不可用as代替which)他获得了诺贝尔化学奖，这使他名扬天下。
(5)当定语从句位于主句之后，纯粹表示主句所述的内容，不带有“如……那样”的意思时，往往用which, 而不用as。
例 20 They were invited to the state banquet, which(as) was a great honor to them. 他们被邀请参加国宴，这对他们来说是莫大的荣幸。
例 21 We had to sleep in our wet clothes, which was most uncomfortable. 我们不得不穿着湿衣服睡觉，这简直太不舒服了。
(6)当定语从句有“如同……那样”的含义时，用as比用which更常见，而这些从句几乎成为固定说法。
例 22 Things will turn out contrary to one’s wishes, as is often the case. 事与愿违，这是常有的事。
例 23 As was natural, this inordinate hope was followed by an excessive depression.这种过分希望之后，接着是极度的沮丧，是很自然的事。
例 24 The material is elastic, as is show in the figure. 这种材料有弹性，如图所示。
例 25 As we know. 众所周知。
例 26 As has been said above/ before. 正如前文所述 。
(7)当定语从句的关系代词指的是先行词本身时，只能用which。
例 27 These apple trees, which I planted tree years ago, have not borne any fruit.这些苹果树是我三年前种下的，没结出任何果实。
例 28 The Thames, which is now clean enough to swim in, was polluted for over a hundred years.泰晤士河，现在已经很干净，可以在里面游泳，它曾被污染了一百多年。
(8)带介词的典型的定语从句，必须用which，不能用as。
例 29 There is a great deal of oxygen around us, without which we could not live. 我们周围有许多氧气，没有它我们就无法生存。
例 30 The shed in our garden, in which we often played, has lasted for a long time. 我们经常玩耍的花园里的那个棚子，已经有很长时间了。
(9)as常与从句中的know，see， hear，expect等动词连用，也常用于as often happens，as is often the case(常有的事)等句子中;而which一般不用于以上情况。
例 31 As is well known，Shanghai is a big city.
(10)当后置的非限制性定语从句是否定结构时，只能用which引导。
例 32 The result of the experiment was very good, which we hadn’t expected.
2. 引导限制性定语从句时which与as的区别：
(1)先行词如果是表示物的名词或代词，在从句中又做介词的宾语时，只能用which。
例 33 This is the pan in which I boiled the milk. 这就是我煮牛奶的锅。
(2)前面有as时,引导定语从句的关系代词用as, 不用which。
例 34 There are as many dictionaries as are needed.所需要的字典都有了。
(3)前面有such时，引导的定语从句的关系代词用as, 不用which。
例 35 Such women as know Tom thought he was charming. 认识汤姆的女人都认为他很迷人。
例 36 I have never heard such stories as he tells. 他讲的那些故事我从没听过。
(4)前面有the same时，引导定语从句的关系代词用as而不用which。
例 37 We are facing the same problems as we did years ago.我们正面临着和多年以前同样的困难。
例 38 This is the same wallet as I lost. 这只钱包与我丢失的那只相同。
(5)单个词引导限制性定语从句时，一般不用as而用which和that。由于关系词在从句中作宾语，which和that都可以省略。
例 39 The project which/that a British businessman has invested in is under construction at present.
(6)“介词+关系代词”引导定语从句时，只能用which。
例 40 Recently I bought an ancient Chinese vase, the price of which was very reasonable.
注：此时的which不能用as来代替。另外还应注意：引导定语从句时，which不能单独作定语，此时不管先行词是人还是物，都只能用whose引导，但指物时，可以用of which替换。
