A stands out most to me, CO comes from the air and air is basically oxygen we breath. When we exhale CO comes out (of course). I would say A is correct.
I would say that you would need to see what the environment around the area is. and what kinds of animals would be out of homes.<span />
I think that since it lives on the ocean floor, at the deepest of the ocean. So anyway, the fin on the Eurypterids is still necessary but not that much, since they live on the ocean floor. Their movements mostly on the ocean floor. So fin would not help them "stick" to the floor. Also there are still gravity acts on the Eurypterids and the feet would help them move faster. Hope this helps.