Grammar
A) "Because of....+ so....." is impossible?When you are using “Because of”, you have already started a sentence with a “because/so” structure, that is, a conditional sentence.
In this case the “so” is not necessary since in a conditional sentence, you can only use either “because of” or “so” , but not both.
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B) "Although...., but....., therefore.........." is possible?
Normally when you use “Although”, you should not use “but”. However in the sentence structure you listed, there could be a lot of variance after the word “Although” which may change the sentence structure. If the sentence structure is changed then using a “but” in the next section of the sentence is possible.
Example :
Although he worked hard he did not pass the examination, but he did not give up and continue study, therefore at the end he became number one in his class
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