@ khadija ...
I was confused to opt between IR and Pol.science , as i haven't studied any of these as a course , so after through discussions and guidance from my seniors , i opted for IR . IR also helps you in preparing Current affairs and pakistan affairs and vice versa . Same was the same with const.law and Int.Law , i opted for int.law ..
It's your decision to choose , as its my first time to appear in CSS ... Go through the course outline in syllabus for the subjects
best of luck