The pollution of the environment (is/ represents/ constitutes) a great danger to our health.

I think all options are OK, but I want to know which choice is the best .

Omar Ahmedwhich choice is the best

I think they are all good. You have shown them in order of formality. "is" is least formal. "represents" and "constitutes" are more formal. In speaking to a friend I'd use "is". In an academic essay I'd use "represents", or maybe "constitutes".