I'm still doing my A-levels, but when it came to choosing my subject to study in uni, i had (still have) no idea!
I went to visit a professor. He said you don't need to pick a specific subject that will determine your career. Pick a general subject that will satisfy many possible careers. In science you could study physics (not so popular so easy to get in), chemistry, maths etc. and in the masters degree you can choose a more specific subject.
this broadens the places you can study. I wanted to study Energy Systems, but the only place you could study it in English was in England (i live in Finland, and England university cost like hell), but with physics i can study here where i live (in Finland education is practically free).
So yea if you not sure, apply for a general subject that interests you, which will buy you more time to think about your career.
Hope this helps