连词和介词用法（CONJUNCTION AND PREPOSITION USES）
1. （表示两件事情同时发生）当…的时候，在…的同时
If something happens as something else happens, it happens at the same time.
2. 像…一样
You use the structure as...as when you are comparing things.
3. （强调数量）多达，只有
You use as...as to emphasize amounts of something.
4. 作为；当作
You use as when you are indicating what someone or something is or is thought to be, or what function they have.
5. 还是…的时候
If you do something as a child or as a teenager, for example, you do it when you are a child or a teenager.
6. 同样地；一样地；像…一样
You use as to say how something happens or is done, or to indicate that something happens or is done in the same way as something else.
7. 因为;作为（结果）
You use as in expressions like as a result and as a consequence to indicate how two situations or events are related to each other.
8. （引导短从句）正如，就像
You use as to introduce short clauses which comment on the truth of what you are saying.
9. 因为；由于
You can use as to mean 'because' when you are explaining the reason for something.
You can use
as,
because,
since, or
for to give an explanation for something.
Because is the commonest of these, and is used when answering a question beginning with 'why?'.You can use
as or
since instead of
because to introduce a clause containing a reason for something, especially in writing.
...a note about The National Portrait Gallery, as the word 'Gallery' can be misleading... Since the juice is quite strong, you should always dilute it. In stories,
for is sometimes used to explain or justify something.
He seemed to be in need of company, for he suddenly went back into the house. Note that
because is a conjunction, and is used to link two ideas within one sentence.
I'm unsocial, because of my deafness.as, because, since 和 for 都可以表示“因为”。because 最常用，往往用来回答以why开头的疑问句。
as 和 since 尤用于书面语中，可以代替 because 引导原因从句。如：a note about The National Portrait Gallery,
as the word ‘Gallery’can be misleading（对 The National Portrait Gallery 的注释，因为 Gallery 一词易产生歧义），Since the juice is quite strong, you should always dilute it（这果汁很浓，你应该把它冲淡一些）。在讲故事时，for 用来解释或证明某事。如：He seemed to be in need of company, for suddenly he went back into the house （他看上去需要有个伴，因为他突然又回到屋里去了）。注意，because是连词，用于连接一个句子中的两个部分，如：I'm unsocial, because of my deafness （由于失聪，我不喜欢社交）。
