Common mistakes made by students

As...so

Example:

1. As my checking account was low, so I had to transfer some money into it.

2. As my checking account was low, I had to transfer money into it.

3. My checking account was low, so I had to transfer money into it. 

Which answer is wrong?

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Answer: (highlight the space between the arrows)

>>Answer is 1. In English you use either "as" or "so", not both.<<

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