The Environmental Protection Agency frequently puts mandatory controls on toxic substances that present as little risk as one in a million chances to cause cancer

A) as little risk as one in a million chances to cause

B) as little risk as one chance in a million of causing

C) as little risk as one chance in a million that it will cause

D) a risk as little as one chance in a million for causing

E) a risk as little as one chance in a million for it to cause

I chose A, which is incorrect. B is the OA. Could someone explain why A is wrong?

How many chances are we discussing - one or a million? In this case, we're trying to say something about the one chance, so "chance" should be singular and go with the word one.