The four outermost planets are Jupiter, Saturn, Uranus and Neptune.
Jupiter is a gas giant, which means it's made of gas and dust helming together by Jupiter's gravity.
Saturn is also a gas giant.
Neptune and Uranus are also gas giants, but included with the dust and rocks making up their surface, they also have a lot of ice, because they are so far from the sun.
The correct answer is B, gas.
