有一次在约有六十人的四级班上问一个分词独立主格结构的句子是什么语法结构，居然没有一个人能够回答。一位高中生问他的老师什么是分词独立主格结构，老师居然给的是一个分词作伴随状语的例子。因此觉得有必要好好讲一讲了。
  首先，在书面英语中两个独立的句子如果是用逗号分开，这就犯了一个典型的错误叫“逗号分裂式”。如：(1) He is sitting before his desk, he is writing a letter. 或 (2) The students were divided into three group, each group had five persons. 就是两个典型的“逗号分裂式”。 修改的办法就是加上一个连词：(1) He is sitting before his desk and he is writing a letter. (2) The students were divided into three group and each group had five persons. 换句话说，书面英语中两个独立的句子必须用连词将两句话连接起来。就第一句(1)而言，修改后的句子虽然没有了“逗号分裂式”的错误，但读来有些累赘，完全可以把它写得紧凑些。由于（1）中前后两句的主语相同，就可以改写为：Sitting before his desk, he is writing a letter. 这里我们作了两个修改：一是去掉了前一句的主语he与助动词is; 二是去掉了连词and。我们把sitting before his desk这一部分称作“分词作伴随状语”。注意：这个分词动词的动作执行者，或者叫逻辑主语是后面的he。需要着重说明的是，如果后面的主语不是分词的动作执行者，那么就犯了另外一个语法错误，即“悬垂分词”。如句子(1)写成：Sitting before the table, a letter is being written. 就犯了典型的“悬垂分词”的错误， 因为 letter不是动作sitting的执行者（信是不能自己坐的！）。看一个高考例题吧：
While building a tunnel through the mountain, _________
a. an under ground lake was discovered.
b. there was an underground lake discovered.
c. a lake was discovered underground.
d. the workers discovered an underground lake.
  这里选择答案的主要标准就是要看四个选项中哪一个的主语可以是building的动作执行者。答案只能是d，因为只有workers才能build。
  再看第二句，(2) The students were divided into three group, each group had five persons. 细心的你会发现句(2)与句(1)的不同。即前后两句的主语不相同。要想把第二句写得紧凑一点(说穿了就是要去掉连词and)的办法是：去掉连词，把后面一句的动词had改成having. 也就是改成：The students were divided into three group，each group having five persons. 这后面的each group having five persons就叫“分词独立主格结构”。之所以称为“独立”主格结构是因为它不像分词作伴随状语那样对主句中的主语有“依赖”。它有自己的动作执行者（这句话里就是each group）。由于不是独立的句子，这个动作的执行者不好称为“主语”只好叫“主格”。所谓“分词独立主格结构”是也。出几个关于“分词独立主格结构”的题目给大家做做吧, 答案请各位给在评论里（正确答案我过一两天公布）。
1______, a man who expresses himself effectively is sure to succeed more rapidly than a man whose command of language is poor
A. Other things being equal 
B. Other things were equal 
C. To be equal to other things
D. Other things to be equal

9． _______, we had to stay at home all day.
[A] The day being very cold    [B] While a very cold day
[C] It was a very cold day     [D] Being a very cold day