The system seems to be working the most efficiently that it has ever worked.

请问这个句子中的 that 从句是什么从句？句子是什么意思？

【答】that 从句是定语从句，修饰efficiently，也就是说， efficiently 是先行词。在主句中，efficiently 是方式副词作状语，the most efficiently 是最高级形式。

▲首先肯定，这句话是正确的。从这个定语从句可以看出，传统语法书中讲的定语从句，先行词仅限于“人，物，时间，地点”，这些概念往往属于名词范畴，没有涉及副词也可以充当先行词，也可以被定语从句修饰，例如作状语的“方式副词”。看来，先行词应该更加多样，范围更加广泛，不仅仅限于“人，物，时间，地点”。因此，语法书需要增加这一条规则。

回到网友的问题：

1. 先行词efficiently 在主句中作方式状语，指代它的关系副词that，在定语从句中同样作方式状语。

2. 修饰副词的定语从句，关系词用that，不用which，而且that可以省略。

3. the most efficiently 中的the 不可省去，因为它被定语从句修饰和限定，要特指。

4. 【翻译】看起来，该系统这次似乎是运行以来最有效的。

含义是：这个系统运行一直有效，这次似乎看起来最有效。

5. 类似例句剖析：

（1）The closest that Herpin came to resting was to sit in a rocking chair and read some newspapers.

1）这个句子的核心词组是：come close to doing  意为“接近做某事”，引申为“趋于做某事”，“愿意做某事”。

2）the closest 是最高级形式：come the closest to doing ，“最愿意做某事”。

3）the closest 成为先行词，被提前。副词的最高级之前加 the，已具备了名词的作用，that Herpin came to resting 充当了定语从句。

4）【翻译】埃尔潘最喜欢的休息方式，是坐在摇椅上读报纸。

（2）The earliest we arrived there was about three days later.

= The earliest time that we arrived there was about three days later.

= The earliest time when we arrived there was about three days later.

we arrived there 是定语从句，先行词是The earliest，省略了关系副词when 或that。

▲ 从以上例句可以看出，副词也可以有自己的定语从句。此外，其最高级形式已具备了名词性质，还可以作句子的主语。

【题外话】传统语法对于表达“时间”的先行词，修饰它的定语从句仅限于使用when 来引导，属于语法规则的遗漏，令人遗憾。其实，现实语言中远不是这样的。

除了when 能引导定语从句外，before, after, since 同样可以引导。请看我的例句和分析：

1. The woman loves to look back upon the time before she got married.

这位妇女喜欢回忆结婚前的那段时间。

2. After sunset, I hate the time before you come home.

日落后，我最难熬您回来以前的这段时间。

3. She made provision for the time after she stopped working by saving money while she worked. 

她工作时就攒钱为退休后的生活作准备了。

4. They relish the time before and after the committee work is done.

他们很喜欢委员会工作完成前后的这段时光。

5. In the time before books appeared, children learned fairy tales by listening to them over and over again.

在书籍出现之前的年代里，孩子们通过反复倾听童话故事而得知里面的内容。

6. He has been a brick during the time since my husband was put into prison on an unjust charge.

自从我丈夫坐冤狱以来，他算得上是一位处患难而不弃的大好人。

7. For most of the time since he died, the first interpretation has appeared to predominate.

自他去世以来的大部分时间里，第一种看法似乎占了上风。

8. She recalls the time before she knew him, and it was so wonderful. 

她回忆起认识他之前的那段时间，那是多么美好啊。

9. For most of the time since it gained independence, the country has been ruled by the cruel man. 

在获得独立后的大部分时间里，该国一直被无情的人所统治。

10. The day before the wedding was held, Anna wept all night. 

在婚礼举行的前一天，安娜哭了一夜。

【分析】when, since, before, after 这4个词，引导定语从句后，不再叫“从属连词”，而是叫“关系副词”。这4个关系副词，表达的意思不同，区别如下：

1. when 侧重定语从句跟先行词时间的重合，至少是有重合点。

如：I shall never forget the day when I was admitted into the Party. 我永远忘不了我被接受入党的那一天。（the day 假设是“7月1日”，我就在这天入党。）

2. since 把先行词的时间，限制在since 从句发生以来的范围。

如：For most of the time since it gained independence, the country has been ruled by the cruel man. 在获得独立以来的大部分时间里，该国一直被无情的人所统治。

3. before 把先行词的时间，限制在before 从句发生之前。

如：She recalls the time before she knew him, and it was so wonderful. 她回忆起认识他之前的那段时间，那是多么美好啊。

4. after 把先行词的时间，限制在after 从句发生之后。

如：She made provision for the time after she stopped working. 她为退休后的那段时间的生活作准备了。