By the early 1940s, tractor design had progressed to the stage where a hydraulic lift system had been developed, as had the power take-off shaft used to drive trailed implements such as a self-binder or a manure spreader.

as 直接接动词，as 和 had 之间省略的主语是什么？as 在这里是什么意思？

【翻译】到20世纪40年代初，拖拉机的设计已经发展到液压悬挂系统的开发阶段，正如动力输出轴被用来驱动牵引装置那样，例如自动收割机或施肥机。

【分析】本句特点：

1. 农业机械专业术语较多。

2. 在stage 后有一个定语从句：where a hydraulic lift system had been developed

3. as had the power take-off shaft...是一个表示方式或比较的“倒装句”：as + 助动词 +主语 + 谓语和其他部分。

该倒装结构，有两种翻译法：

（1）正如......那样；（2） ......也是如此。

4. 本句使用正常语序也可，意思不变：

as the power take-off shaft had been used to drive trailed implements such as a self-binder or a manure spreader  正如动力输出轴被用来驱动牵引装置那样，例如自动收割机或施肥机。（as：正如......那样）

不过，我认为，该句漏掉了一个词：been，因为是被动语态the power take-off shaft had been used to drive（被用来驱动），had 已提前构成倒装。请核对原文。

关于这种倒装句的详细情况，请参见我以前的一个解答：

http://ask.yygrammar.com/q-7472.html

同意曹/黎老师解答，这老师 as 引导方式状语的倒装结构

A: as引导方式状语从倒状语

(1)as +助动词+主语
“as +助动词+主语”结构中的助动词主要是指助动词do
The delicious and vast menu choices contribute to the popularity of the Indian restaurant, as does the authentic and quaint décor.（does 代替前面谓语动词，属于全倒装结构）

=The delicious and vast menu choices contribute to the popularity of the Indian restaurant, as the authentic and quaint décor contribute to the popularity of the Indian restaurant,

这家印度餐馆生意很火，既因为其美味多样的菜肴，也因为其原汁原味的独特装饰。

She has seen the film, as have I .

He had seen the film, as had I .

(2)as＋ be动词＋主语
As引导的方式状语从句除了会出现代替主句谓语部分的助动词do的各种形式外，还会出现be动词的各种形式。
Short-term memory is weakened, as are abilities to make decisions and to concentrate.

=Short-term memory is weakened, as abilities to make decisions and to concentrate are weakened.

正如决策能力与专注能力降低一样，瞬时记忆能力也会降低。

B:as引导让步状语从句倒装结构

as  引导的让步从句必须将表语或状语提前 （形容词,  副词,  分词,  实义动词提前）。　

注意：

(1)句首名词不能带任何冠词。
(2)句首是实义动词,  其他助动词放在主语后。如果实义动词有宾语和状语,　 随实义动词一起放在主语之前。

Try  hard as he will, he never seems able to d o the work  satisfactorily.

具体形式如下

as可引起让步状语从句，表示“虽然、尽管”，但要用部分倒装结构，形式如下：

1.  形容词 + as +  主语 +  系动词。

Tired  as he is, he offers to help me.

尽管他已经很累了，他还是主动提出帮助我。

2.  过去分词 + as +  主语 +  系动词。

Well-written  as the book is, the author is not satisfied and prepared to revise it.  

尽管这本书写得很好，作者还是不满意并打算修改它。

3.  名词 + as +  主语 +  系动词。

Student  as he is, he does not study hard.

他虽然是个学生，却不努力学习。

4.  副词 + as +  主语 +  谓语部分。

Much as  I admire his courage, I don’t think he acted wisely.

我虽然崇拜他的勇气，但我认为他这样做是不明智的。

5.  动词原形 + as +  主语 +  谓语的另一部分（情态动词或助动词may,  might, will, would等）。

Try as  you will, you won’t be able to persuade him.

不管你怎么努力，你都说服不了他。

备注：下面的为正确理解和分析

By the early 1940s, tractor design had progressed to the stage where a hydraulic lift system had been developed, as had the power take-off shaft used to drive trailed implements such as a self-binder or a manure spreader.（had 代替where定语从句的谓语部分）

还原后=By the early 1940s, tractor design had progressed to the stage where a hydraulic lift system had been developed, as  the power take-off shaft used to drive trailed implements such as a self-binder or a manure spreader had been developed

句子语法结构分析如下

时间状语：By the early 1940s,

主句主语：tractor design

主句谓语：had progressed 

主句状语(1)：to the stage Where a hydraulic lift system had been developed, as had the power take-off shaft used to drive trailed implements such as a self-binder or a manure spreader.

修饰名词定语从句：Where a hydraulic lift system had been developed

修饰定语从句谓语的方式状语(2)：as had the power take-off shaft used to drive trailed implements such as a self-binder or a manure spreader.

重点单词和短语解析如下：

(1)hydraulic lift system  液压悬挂/提升系统

(2)take-off shaft  输出传动轴

(3)shaft (机械的)轴，传动轴

(4)trailed  implement 牵引式农机具

(5)trailed  adj. 被牵引的

(6)implement   n.工具;器具;用具

(5)self-binder  n. 自动割捆机

(6)manure spreader  n. 撒肥机；撒厩肥机

(7)By the early 1940 截止到二十世纪四十年代初期

(8)tractor design 拖拉机设计

(9)be progressed to 进步/进展/发展改进到

【问】 By the early 1940s, tractor design had progressed to the stage where a hydraulic lift system had been developed,

as had the power take-off shaft used to drive trailed implements such as a self-binder or a manure spreader.

    as 直接接动词，as 和 had 之间省略的主语是什么？as 在这里是什么意思？

【答】

1. 关于译文：（抛砖引玉）

二十世纪四十年代初，拖拉机的设计已经发展到了液压传动的阶段，用于驱动诸如收割机或施肥机等牵引机械的动力输出轴也已经发展到了同样的阶段。

2. 关于as 的词性和意义

as 为连词。 LDOCE 给as 的这一用法专门列出一个义项：used to add that what you have said is also true of someone or something else（用于表示另一人或另一事物“也如此”）。as 相当于and so，与连词neither 或nor 构成反义词。例如：

He wanted to leave, as did I/ and so did I.(他想离开，我也一样)

    也有学者将此as 归入方式状语连词，但这并不重要，重要的是了解其用法。

3.关于 as 倒装句的结构

用于此义的as 倒装句的基本结构为：“情态/助动词/be+主语”结构（主语后不再出现动词）。即使时态不同亦如此（恕不详叙）。例如：

After a brief period of office work, Mann devoted himself to writing, as had his elder brother Heinrich.(Britannica Concise Encyclopedia).

(不说as had his elder brother Heinrich devoted…)

4. 句子结构分析：

4.1 前半部分：

By the early 1940s（状语）, tractor design（主语） had progressed to the stage（谓语部分）where a hydraulic lift system had been developed（定语从句）

4.2 后半部分：

as(连词) had（助动词）the power take-off shaft（主语）used to drive trailed implements such as a self-binder or a manure spreader（过去分词短语定语）

5. 句子分析说明：

1. as 引导的倒装句谓语只保留前置的助动词had，习惯上在主语之后不出现实义动词（progressed） 。（此话题恕不详叙）

2. used to drive…是修饰主语power take-off shaft 的定语，不是谓语组成部分,因此不存在been缺漏的问题。否则结构和句意都不符合逻辑。

3. 鉴于以上分析，as 句不可改写为如下正常语序：as the power take-off shaft had been used to drive trailed implements such as a self-binder or a manure spreader。

    不倒装的正常语序应该为：as the power take-off shaft used to drive trailed implements such as a self-binder or a manure spreader had done.

    但这样的句子因主语部分过长，导致头重脚轻，违背了英语末端重心的原则，不是地道的表达方式。