托福阅读长难句

Spiral galaxies are well supplied with the interstellar gas in which new stars form; as the rotating spiral pattern sweeps around the galaxy it compresses gas and dust, triggering the formation of bright young stars in its arms.

【子句拆分】

连接词：in which
定语从句：In the gas new stars form.
连接词：as
状语从句：The rotating spiral pattern sweeps around the galaxy.
并列句1：It compresses gas and dust, triggering the formation of bright young stars in its arms.
并列句2：Spiral galaxies are well supplied with the interstellar gas.

【成分划分】

定语从句：In the gas[状语] new stars[主语] form[谓语].
翻译：新的星球会在星际间的气体中形成。
状语从句：The rotating spiral pattern[主语] sweeps[谓语] around the galaxy[状语].
翻译：旋转的螺旋型围绕星系扫过。
并列句1：It[主语] compresses[谓语] gas and dust[宾语], triggering the formation of bright young stars in its arms[状语].
翻译：它会挤压气体和尘埃，从而在旋臂中促成明亮的年轻星球的形成。
并列句2：Spiral galaxies[主语] are well supplied[谓语] with the interstellar gas[状语].
翻译：螺旋形的星系被星际间的气体很好地补给。

【全句翻译】

螺旋形的星系被星际间的气体很好地补给，新的星球会在星际间的气体中形成；当旋转的螺旋型围绕星系扫过的时候会挤压气体和尘埃，从而在旋臂中促成明亮的年轻星球的形成。

知识点梳理

这句话中的 triggering the formation of bright young stars in its arms 属于动词ing形式作结果状语， the rotating spiral pattern sweeps around the galaxy it compresses gas and dust 属于原因，前后构成因果关系。
例句：The song is sung all over the country, making it very popular.