Which pair below expresses the same relation as Oasis : Desert, completing the analogy?

An oasis is a small watered green spot set in the middle of a vast dry waste — a patch of the very opposite character, ringed about by the expanse. An island stands in exactly that way to the ocean, a small patch of dry land ringed about by water. 'Dune : Sand' and 'Sand : Beach' both join a thing to the stuff it is made of or helps to make, which is a wholly different tie. 'Camel : Desert' names a creature and the country it lives in, and the camel is at home in the sand rather than a contrast to it.