Sorry for replying you late. I am also a student of Civil Engineering, Islamic history and culture is a good one. Why don't you opt Applied Maths ?
I mean we engineers are good at it, apart from that, you can also have a look at Physics. I have just completed my first year in Engineering and can gauge that I can easily do Paper I of Physics.
You know why we engineers are not that prominent in CSS examination ?
Its because, when it comes to CSS, we leave our main subjects, Maths and Physics.
Try to have a look at the syllabus and then if you feel, you are not comfortable with it. You can go for the above mentioned subjects.