1. The Earth was formed about five billion years ago from a rotating, circular cloud of dust and gases such as hydrogen and nitrogen.
    地球的形成约在50亿年前，起源于一团循环旋转的尘埃和诸如氢、氧之类的气体。

2. Nitrogen forms four-fifths of the atmosphere.
    氮气占空气的五分之四。