Dear Monika,
You have made a good decision by opting for B.A as you aspire to become IAS officer. The decision over choosing the subjects in graduation is solely your internal matter. You have to decide which subjects should be choosen for study.
Well i can further tell the subjects which will help you in your foundation for UPSE:

• Indian history
• Public administration
• Geography
• Political science
• Economics

The subjects mentioned above are also in the list optional paper if you select any of these subjects as a graduate subject then it will help you in building toward your aim.
ALL THE BEST.