What A level should i do?

So far, i have decided that i would like to do history and maths, but i dont know what else :frown:

My other choices are biology, chemistry and physics.
Im more interested in doing physics, which means that for my fourth A level, im stuck between deciding whether to do biology or chemistry. I cant pick one relevant to my career aspiration/uni course, because i dont know what i would like to do. Im interested in the fields of history and science though. I enjoy all of the subjects equally.
Im aspiring to go somewhere like Oxford/Cambridge, and my teacher to me that chemistry is a harder A level than biology, so would taking chemistry increase my chances of getting in? But she also said that biology is kinda more relevant with jobs and all; there are more jobs in biology, governments dont fund as much for physics research, etc.
What A levels would you recommend? Would picking specific A levels help to go to a good uni, or open more doors? thanks