Wow! Environmental science isn't a very common a level- you're very lucky to be able to take it if that what you'd like to do! I think perhaps chemistry would be a better option since the environment does contain a lot of biological, chemical, and, of course, biochemical goings on. If possible I suggest doing both if you can and more importantly, want to and think you're capable! Personally, if I were scientifically inclined (I was last year but my new teacher ruined my passion for biol), then I would pick biology and chemistry on top of those two choices since they compliment them the best. But that's what I find interesting haha! I now want to do french so things change