You can use because, as, 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.

because, as, since 或者 for 都可以用来给出解释。because 最常用，用来回答以 why 开头的疑问句。as 或 since 可以代替 because 引导原因从句，尤其是在书面语中：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 一词容易令人误解），Since the juice is quite strong, you should always dilute it（这种果汁太浓，所以必须加以稀释）。在故事中，for有时用于解释或论证：He seemed to be in need of company, for he suddenly went back into the house（他看起来需要陪伴，因为他突然回到了屋里）。注意，because 是连词，用来连接一个句子中的两个观点：I'm unsocial, because of my deafness（我耳朵聋，所以不善交际）。