In my opinion, you should go to computer science and physics because you have background and this will help you in scoring greater number than I.R. as both are science subjects. Then questions appear about overlapping topics of PA and CA , overlapped topics can easily prepared, we all studied in day to day like kashmir issue, nuclear issue, dam issue, hydropolitics and others. You may cover these topics by reading newspaper daily. Current affairs and Topics of PA are contemporanous in nature and only source of information would be newspaper and helps in eassy also.
Now you can imagine future when you keep science subjects.
You scored 160 + in both and you will also get allocated in prestigious group. There is time of 7 months for 2020. This is enough time to study.

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