The universe could be considered an isolated system because
1many people think that no energy or matter exists outside the universe.
2energy and matter are created in the universe and flow freely into and out of the universe.
3 energy is created outside the universe and matter is created within the universe.
4energy is created in the universe and matter is transferred out of the universe.

gets less

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.