句子結構的概念
句子的要素
一個句子只能有一個主詞跟動詞，這是句子最基本的要素。沒有主詞（除了祈使句省略you)，就不是句子; 同樣地，沒有動詞也不是句子。這樣的句子，就叫做簡單句。下面先舉出幾個簡單句的例子，在句中，主詞畫底線，而動詞用粗體字標示出來。
- Last Friday, David got up too late.
- His mother took him to school by motorcycle.
- On the way, they had an accident.
- David was hurt badly.
- His mother sent him to the hospital.
- She called his teacher.
- She asked for a sick day off for David.
用連接詞讓句子變長
如果一個句子要出現兩個動詞，動詞就必須變形為不定詞、現在分詞、過去分詞或原型。而作者為了讓文章中句子長短間錯，或呈現前後兩個句子間的關係，可以用連接詞連接。接下來，我們將上面的例句用適合的連接詞合併起來。（動詞用粗體，而連接詞以底線標示出來）。
- Last Friday, David got up too late, so his mother took him to school by motorcycle.
- On the way, they had an accident, and David was hurt badly.
- After his mother sent him to the hospital, she called David’s teacher and asked for a sick day off for David.
如上面所示，使用連接詞，可以讓兩個句子之間的關係變得比較明顯清楚，也可讓文章的句子長短交錯，比較有趣。
我們可以用以下的方法連接兩個句子：
- 使用對等連接詞–for, and, nor, but, or, yet, so
- 使用從屬連接詞–because, (al)though, when, after, before, as, while, if, whether, until, unless
- 使用關係代名詞和關係副詞–who, whom, which, that, what, when, where, why, how
- 使用分號–當兩個句子關係密切，卻找不出一個適當的連接詞，或想要用副詞轉換詞，讓文章句型多變化，可以用分號當連接詞。(想要讓文章句型多變化，還有很多方法，請閱讀『如何寫出多變化的英文句子』）
注意到了嗎？逗號不能用來連接兩個動詞或兩個句子。這一點就是導致大部分學生判斷錯誤的最大原因。
some of which和some of them這一類題型解析
some of which，some of whom 或some of them
由上面的解說可知，which和whom是關係代名詞，可以連接兩個句子。在形容詞子句的補述用法中，which, who, whom所帶領的句子要用逗號和前面的名詞隔開，並且可以位於句子中。some of which與some of whom就用在補述用法中，所以前面要有逗號; 而them是代名詞，不可以連接兩個句子，可以打句號，分成兩句，也可以在前面句子後打分號當連接詞。（點擊鏈結，可以進一步了解形容詞子句的限定用法與補述用法）
下面舉一些例子來說明（兩個句子中的逗號、分號和them會用粗體，連接詞會用底線標示）：
- At the zoo, the teacher saw her students, some of whom held a balloon in their hands.
- They found those sick monkeys, some of which were dying, in the cave.
- These singers, some of whom are popular with young students, will join the contest.
上面這三個例子，都是用關係代名詞whom跟which來連接兩個句子，用逗號與前面名詞隔開。現在，將其中的which 跟 whom改寫成them，請注意標點符號的變化，還有them在句子位置的改變。
- At the zoo, the teacher saw her students; some of them held a balloon in their hands.
- In the cave they found those sick monkeys; some of them were dying.
- These singers will join the contest; some of them are popular with young students.
雖然，在這裡，我們說可以用分號當連接詞，再加上some of them，可是，在寫作時，最好不要這樣做，簡單以句號隔開兩句就好。分號要用的少，用的好，考試時，會讓作文增色不少。（請參考『英文標點符號的用法』一文
這種在關係代名詞前面加上量詞的題型包括:
- one of which, one of whom, one of them
- many of which, many of whom, many of them
- a few of which, a few of whom, a few of them
- most of which, most of whom, most of them
after which 或 after that
在形容詞子句的非限定用法中，which可以用來代替前面一整個句子的語意，也就是一件事。在寫敘述文的時候，我們常常會說在那件事之後，這在英文有許多手法來表達，而after which 跟after that 就是其中兩種，也是考試常造成疑惑的選項。
看到這裡，想必讀者可以清楚的知道，什麼時候用after which？什麼時候用after that？下面一樣舉出幾個例子，將兩者做改寫，請注意after which跟after that前面的標點符號。
- The boy had a severe accident at the age of six, after which, he was unable to speak.
- He went into a haunted house alone one night, after which, he was afraid to be in the dark alone.
同樣地，我們將例句中的after which改寫成after that，請注意標點符號的變化。
- The boy had a severe accident at the age of six; after that, he was unable to speak.
- He went into a haunted house alone one night; after that, he was afraid to be in the dark alone.
同樣地，雖然可以用分號當連接詞，再加上after that，但是，很少人這麼做，最好簡單以句號隔開兩句就好。
原來，這麼讓人困擾的文法題型，只要注意標點符號就能解決，沒想到標點符號在英文中有這麼大的功用吧！趕快找一些練習題來練習，多應用便能將這個觀念記下，考試的時候，就會非常清楚選擇哪個答案才對。
如果你有其他文法上的疑惑，可以到我們『英文文法』專頁，看看有沒有文章探討相關文法問題。
