要理解这个问题，首先要明白“主谓宾定状补以及同位语”的含义，以及他们在句子中的位置、所起的作用等。在常见的英语句中，主谓宾是不可缺少，但在祈使句中常常省略主语，如，(You) Don't walk./(You) Come here. 这类句子一般表达命令、请求、建议等。下面是每种成分的具体解释：
英语句子的成分共九类，其中最主要的句子成分包括：主、谓、宾、表、定、状、补语和同位语。
1. 主语 (Subject) 是句子的核心，是人或事。
a) 位置：通常位于句子的开头或位于谓语动词前，表明动作的主体。
b) 可以作主语的成分包括：名词、代词、数词、主语从句(what/that/ how/ whether从句等)、现在分词(-ing) 和动词不定式(to do)、the + adj.结构。
c) Study the following examples and underline the subject in each sentence.
Eg1. An earthquake has claimed hundreds of lives.
Eg2. Whether the football game will be played depends on the weather.
Eg3. The ignorant can be fearless.
2. 谓语 (Predicate) 用来描述主语的动作、状态或特征。
a) 位置：通常紧接着主语。
b) 可以作谓语的成分包括：动词、情态动词+动词。
c) Study the following examples and underline the predicate in each sentence.
Eg1. Life is full of ups and downs.
Eg2. You cannot control your life, but you can control your attitude towards life.
Eg3: In this day and age, an increasing number of people agree that gambling (赌博) is an unwholesome hobby.
3. 宾语 (Object) 用来表示动作或行为的对象。
a) 位置：位于及物动词或介词后面。
b) 可以作宾语的成分包括：名词、代词、数词、复合结构(双宾语等)、从句(what/that/ how/ whether从句等)、现在分词、动词不定式。
c) Study the following examples and underline the object in each sentence.
Eg1. Junk food impairs people’s health.
Eg2. Change what you can bear, while bear what you cannot change.
Eg3. Studies reveal that there is a definite link between obesity (肥胖症) and serious diseases such as heart attacks.
4. 表语 (Predicative)
a) 位置：位于be动词或系动词 (如：look, seem, 详见《讲义》P8)
b) 可以作表语的成分包括：名词、代词、数词、形容词、副词、介词短语、现在分词、过去分词、动词不定式或从句(what/that/ how/ whether从句等)。
c) Study the following examples and underline the predicative in each sentence.
Eg1. Life is a stage.
Eg2. I feel under the weather today.
Eg3. What we should do is to teach children how to distinguish good from bad (right from wrong).
5. 定语 (Attribute) 用来修饰名词或名词性词组。
a) 位置：通常位于名词或名词性词组之前，有时也可放在之后(I want something to eat)。
b) 可以作定语的成分包括：形容词(最常用)、代词、数词、名词、名词所有格、介词短语、现在分词、过去分词、动词不定式和定语从句。
c) Study the following examples and underline the attribute in each sentence.
Eg1. A warm smile is the universal language.
Eg2. In recent years, the Internet has been gaining in popularity at an amazing rate/ at lightning speed.
Eg3. Those who have spent some time earning a living or traveling to other places, have a broader view of life.
6. 状语 (Adverbial) 用来修饰动词、形容词、副词或整个句子。
a) 位置：通常位于动词、形容词、副词或句子的前后。
b) 可以作状语的成分包括：副词(最常用)、介词短语、名词、动词不定式、现在分词、过去分词、状语从句和状语从句省略结构。
c) Study the following examples and underline the adverbial in each sentence.
Eg1. Outdoor activities can greatly improve our health.
Eg2. Compared with the corresponding period last year, imports in the first three months have increased by 10 per cent
Eg3. When I was young, I was a troublemaker.
7. 补语 (Complement) 对于主语或宾语进行补充说明。
a) 分为主语补足语(补充说明主语的性质或状态)和宾语补足语(补充说明宾语的性质或状态)。
b) 在雅思写作中，主要的宾补结构主要是双宾语结构。
c) Study the following examples and underline the complement in each sentence.
Eg1. I regard you as my best friend.
Eg2. The graduates find the job market frustrating because of the economic recession.
Eg3. The advent of information age makes technical knowledge more crucial than ever.
8. 同位语 (Appositive) 表明句子中的一个成分与另一成分表达同一概念，即A＝B。
a) 可以作同位语的成分包括：名词、代词、数词、形容词、介词短语、从句、动词不定式和现在分词。
b) Study the following examples and underline the appositive in each sentence.
Eg1. We should ask Jim, the monitor, to be punctual.
Eg2. Job satisfaction, a very important part of an employee’s sense of well-being (幸福，安宁), can be promoted in most jobs.
Eg3. All countries, big or small, should be treated equal.
参考资料：http://iask.sina.com.cn/b/20773863.html