原文如下：
The substances that make up both groups of plants are divided into three groups - gases, rocks, and ices - based on their melting points. The terrestrial planets are mostly rocks: dense rocky and metallic material, with minor amounts of gases. The Jovian planets, on the other hand, contain a large percentage of the gases hydrogen and helium, with varying amounts of ices: mostly water, ammonia, and methane ices.
当我做题的时候，我的理解就是把这两个planet分类，交集是gases, the terrestrial planets独有的是rocks顺带少量的气体,the Jovian planets独有的是冰主要是气体，所以两个planet都有气体，但是Saturn 属于one of the outer planets - the four Jovian planets are known as the outer planets, 所以Saturn不应该包含rocks
你再看看，我再想想...
