How to respond some general question in a general way in an interview?

I graduated something else and got an interview for an office job position. This, because my diploma is not valid in the US and I applied different kind of jobs. The questions in the interview: Why you decided to come in an office job position and not pursue your educational career in the US?, How you would respond? And also, couple of general tips to keep in mind! This is my first interview in the US Thanks in advance

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